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 $62.60   5.728%   $66.1857   $66.19   $66.20   $66.20  
  Purchase #2 $150.30   8.387%   $162.9057   $162.91   $162.90   $162.90  
  Purchase #3 $245.45   8.244%   $265.6849   $265.68   $265.70   $265.70  
  Purchase #4 $163.89   11.569%   $182.8504   $182.85   $182.85   $182.90  
  Purchase #5 $165.53   12.578%   $186.3504   $186.35   $186.35   $186.40  
  Purchase #6 $80.97   4.648%   $84.7335   $84.73   $84.75   $84.70  
  Purchase #7 $211.61   3.135%   $218.244   $218.24   $218.25   $218.20  
  7 purchase totals = $1,080.35       $1,166.9546   $1,166.95   $1,167.00   $1,167.00