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 $68.35   10.350%   $75.4242   $75.42   $75.40   $75.40  
  Purchase #2 $220.54   9.340%   $241.1384   $241.14   $241.15   $241.10  
  Purchase #3 $53.44   9.587%   $58.5633   $58.56   $58.55   $58.60  
  Purchase #4 $238.40   9.507%   $261.0647   $261.06   $261.05   $261.10  
  Purchase #5 $164.76   4.690%   $172.4872   $172.49   $172.50   $172.50  
  Purchase #6 $48.59   13.571%   $55.1841   $55.18   $55.20   $55.20  
  Purchase #7 $62.99   10.427%   $69.558   $69.56   $69.55   $69.60  
  7 purchase totals = $857.07       $933.4199   $933.41   $933.40   $933.50