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 $229.86   10.145%   $253.1793   $253.18   $253.20   $253.20  
  Purchase #2 $97.97   8.829%   $106.6198   $106.62   $106.60   $106.60  
  Purchase #3 $112.67   12.287%   $126.5138   $126.51   $126.50   $126.50  
  Purchase #4 $37.26   5.311%   $39.2389   $39.24   $39.25   $39.20  
  Purchase #5 $83.42   3.605%   $86.4273   $86.43   $86.45   $86.40  
  Purchase #6 $190.89   12.805%   $215.3335   $215.33   $215.35   $215.30  
  Purchase #7 $113.94   11.422%   $126.9542   $126.95   $126.95   $127.00  
  7 purchase totals = $866.01       $954.2668   $954.26   $954.30   $954.20