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 $249.70   10.628%   $276.2381   $276.24   $276.25   $276.20  
  Purchase #2 $230.69   8.187%   $249.5766   $249.58   $249.60   $249.60  
  Purchase #3 $9.75   4.496%   $10.1884   $10.19   $10.20   $10.20  
  Purchase #4 $190.57   6.660%   $203.262   $203.26   $203.25   $203.30  
  Purchase #5 $214.36   11.666%   $239.3672   $239.37   $239.35   $239.40  
  Purchase #6 $194.71   5.822%   $206.046   $206.05   $206.05   $206.00  
  Purchase #7 $155.90   4.523%   $162.9514   $162.95   $162.95   $163.00  
  7 purchase totals = $1,245.68       $1,347.6297   $1,347.64   $1,347.65   $1,347.70