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 $231.64   11.356%   $257.945   $257.95   $257.95   $257.90  
  Purchase #2 $125.55   12.727%   $141.5287   $141.53   $141.55   $141.50  
  Purchase #3 $247.31   4.398%   $258.1867   $258.19   $258.20   $258.20  
  Purchase #4 $237.43   9.793%   $260.6815   $260.68   $260.70   $260.70  
  Purchase #5 $199.45   4.730%   $208.884   $208.88   $208.90   $208.90  
  Purchase #6 $92.66   9.461%   $101.4266   $101.43   $101.45   $101.40  
  Purchase #7 $12.61   12.652%   $14.2054   $14.21   $14.20   $14.20  
  7 purchase totals = $1,146.65       $1,242.8579   $1,242.87   $1,242.95   $1,242.80