Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.33   11.402%   $206.4613   $206.46   $206.45   $206.50  
  Purchase #2 $249.57   8.866%   $271.6969   $271.70   $271.70   $271.70  
  Purchase #3 $234.59   11.147%   $260.7397   $260.74   $260.75   $260.70  
  Purchase #4 $203.31   10.711%   $225.0865   $225.09   $225.10   $225.10  
  Purchase #5 $168.55   11.287%   $187.5742   $187.57   $187.55   $187.60  
  Purchase #6 $203.99   7.584%   $219.4606   $219.46   $219.45   $219.50  
  Purchase #7 $248.74   5.332%   $262.0028   $262.00   $262.00   $262.00  
  7 purchase totals = $1,494.08       $1,633.0220   $1,633.02   $1,633.00   $1,633.10