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 $209.62   8.248%   $226.9095   $226.91   $226.90   $226.90  
  Purchase #2 $236.94   10.568%   $261.9798   $261.98   $262.00   $262.00  
  Purchase #3 $35.54   11.208%   $39.5233   $39.52   $39.50   $39.50  
  Purchase #4 $216.43   12.639%   $243.7846   $243.78   $243.80   $243.80  
  Purchase #5 $213.94   11.478%   $238.496   $238.50   $238.50   $238.50  
  Purchase #6 $229.41   11.266%   $255.2553   $255.26   $255.25   $255.30  
  Purchase #7 $230.35   3.296%   $237.9423   $237.94   $237.95   $237.90  
  7 purchase totals = $1,372.23       $1,503.8908   $1,503.89   $1,503.90   $1,503.90