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 $88.82   9.834%   $97.5546   $97.55   $97.55   $97.60  
  Purchase #2 $58.40   3.508%   $60.4487   $60.45   $60.45   $60.40  
  Purchase #3 $173.45   12.434%   $195.0168   $195.02   $195.00   $195.00  
  Purchase #4 $40.46   10.838%   $44.8451   $44.85   $44.85   $44.80  
  Purchase #5 $28.35   11.496%   $31.6091   $31.61   $31.60   $31.60  
  Purchase #6 $107.57   13.332%   $121.9112   $121.91   $121.90   $121.90  
  Purchase #7 $214.32   13.667%   $243.6111   $243.61   $243.60   $243.60  
  7 purchase totals = $711.37       $794.9966   $795.00   $794.95   $794.90