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 $46.39   13.377%   $52.5956   $52.60   $52.60   $52.60  
  Purchase #2 $188.49   9.230%   $205.8876   $205.89   $205.90   $205.90  
  Purchase #3 $122.69   3.306%   $126.7461   $126.75   $126.75   $126.70  
  Purchase #4 $216.57   9.379%   $236.8821   $236.88   $236.90   $236.90  
  Purchase #5 $68.80   11.387%   $76.6343   $76.63   $76.65   $76.60  
  Purchase #6 $136.73   11.128%   $151.9453   $151.95   $151.95   $151.90  
  Purchase #7 $86.37   3.398%   $89.3049   $89.30   $89.30   $89.30  
  7 purchase totals = $866.04       $939.9959   $940.00   $940.05   $939.90