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 $48.33   6.157%   $51.3057   $51.31   $51.30   $51.30  
  Purchase #2 $71.63   13.752%   $81.4806   $81.48   $81.50   $81.50  
  Purchase #3 $114.41   9.431%   $125.2   $125.20   $125.20   $125.20  
  Purchase #4 $87.33   11.791%   $97.6271   $97.63   $97.65   $97.60  
  Purchase #5 $176.37   9.834%   $193.7142   $193.71   $193.70   $193.70  
  Purchase #6 $179.55   12.313%   $201.658   $201.66   $201.65   $201.70  
  Purchase #7 $181.92   7.165%   $194.9546   $194.95   $194.95   $195.00  
  7 purchase totals = $859.54       $945.9402   $945.94   $945.95   $946.00