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 $60.28   10.239%   $66.4521   $66.45   $66.45   $66.50  
  Purchase #2 $89.77   13.290%   $101.7004   $101.70   $101.70   $101.70  
  Purchase #3 $86.54   5.340%   $91.1612   $91.16   $91.15   $91.20  
  Purchase #4 $158.32   9.462%   $173.3002   $173.30   $173.30   $173.30  
  Purchase #5 $59.69   4.276%   $62.2423   $62.24   $62.25   $62.20  
  Purchase #6 $217.36   3.331%   $224.6003   $224.60   $224.60   $224.60  
  Purchase #7 $29.37   3.811%   $30.4893   $30.49   $30.50   $30.50  
  7 purchase totals = $701.33       $749.9458   $749.94   $749.95   $750.00