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 $224.61   9.804%   $246.6308   $246.63   $246.65   $246.60  
  Purchase #2 $64.30   5.231%   $67.6635   $67.66   $67.65   $67.70  
  Purchase #3 $84.59   9.843%   $92.9162   $92.92   $92.90   $92.90  
  Purchase #4 $122.71   10.156%   $135.1724   $135.17   $135.15   $135.20  
  Purchase #5 $141.87   12.579%   $159.7158   $159.72   $159.70   $159.70  
  Purchase #6 $95.92   9.534%   $105.065   $105.07   $105.05   $105.10  
  Purchase #7 $119.36   12.217%   $133.9422   $133.94   $133.95   $133.90  
  7 purchase totals = $853.36       $941.1059   $941.11   $941.05   $941.10