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 $82.96   12.372%   $93.2238   $93.22   $93.20   $93.20  
  Purchase #2 $81.65   8.849%   $88.8752   $88.88   $88.90   $88.90  
  Purchase #3 $48.39   6.450%   $51.5112   $51.51   $51.50   $51.50  
  Purchase #4 $241.83   8.326%   $261.9648   $261.96   $261.95   $262.00  
  Purchase #5 $87.86   7.600%   $94.5374   $94.54   $94.55   $94.50  
  Purchase #6 $207.25   8.105%   $224.0476   $224.05   $224.05   $224.00  
  Purchase #7 $106.84   11.565%   $119.196   $119.20   $119.20   $119.20  
  7 purchase totals = $856.78       $933.3560   $933.36   $933.35   $933.30