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 $28.67   13.712%   $32.6012   $32.60   $32.60   $32.60  
  Purchase #2 $153.63   7.161%   $164.6314   $164.63   $164.65   $164.60  
  Purchase #3 $125.29   10.433%   $138.3615   $138.36   $138.35   $138.40  
  Purchase #4 $70.27   13.733%   $79.9202   $79.92   $79.90   $79.90  
  Purchase #5 $197.72   5.470%   $208.5353   $208.54   $208.55   $208.50  
  Purchase #6 $193.41   11.523%   $215.6966   $215.70   $215.70   $215.70  
  Purchase #7 $75.96   13.158%   $85.9548   $85.95   $85.95   $86.00  
  7 purchase totals = $844.95       $925.7010   $925.70   $925.70   $925.70