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 $44.97   12.545%   $50.6115   $50.61   $50.60   $50.60  
  Purchase #2 $230.82   11.474%   $257.3043   $257.30   $257.30   $257.30  
  Purchase #3 $88.67   5.317%   $93.3846   $93.38   $93.40   $93.40  
  Purchase #4 $125.66   6.423%   $133.7311   $133.73   $133.75   $133.70  
  Purchase #5 $247.71   9.266%   $270.6628   $270.66   $270.65   $270.70  
  Purchase #6 $42.39   9.397%   $46.3734   $46.37   $46.35   $46.40  
  Purchase #7 $130.79   7.438%   $140.5182   $140.52   $140.50   $140.50  
  7 purchase totals = $911.01       $992.5859   $992.57   $992.55   $992.60