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 $69.86   7.731%   $75.2609   $75.26   $75.25   $75.30  
  Purchase #2 $237.88   7.593%   $255.9422   $255.94   $255.95   $255.90  
  Purchase #3 $62.59   7.208%   $67.1015   $67.10   $67.10   $67.10  
  Purchase #4 $200.34   5.306%   $210.97   $210.97   $210.95   $211.00  
  Purchase #5 $14.43   8.581%   $15.6682   $15.67   $15.65   $15.70  
  Purchase #6 $148.40   10.139%   $163.4463   $163.45   $163.45   $163.40  
  Purchase #7 $143.83   5.344%   $151.5163   $151.52   $151.50   $151.50  
  7 purchase totals = $877.33       $939.9054   $939.91   $939.85   $939.90