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 $26.94   10.454%   $29.7563   $29.76   $29.75   $29.80  
  Purchase #2 $161.83   8.604%   $175.7539   $175.75   $175.75   $175.80  
  Purchase #3 $126.61   5.406%   $133.4545   $133.45   $133.45   $133.50  
  Purchase #4 $69.98   9.116%   $76.3594   $76.36   $76.35   $76.40  
  Purchase #5 $83.77   10.184%   $92.3011   $92.30   $92.30   $92.30  
  Purchase #6 $238.92   3.351%   $246.9262   $246.93   $246.95   $246.90  
  Purchase #7 $225.41   5.549%   $237.918   $237.92   $237.90   $237.90  
  7 purchase totals = $933.46       $992.4694   $992.47   $992.45   $992.60