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 $92.34   7.272%   $99.055   $99.06   $99.05   $99.10  
  Purchase #2 $114.61   9.833%   $125.8796   $125.88   $125.90   $125.90  
  Purchase #3 $82.92   11.846%   $92.7427   $92.74   $92.75   $92.70  
  Purchase #4 $21.66   10.378%   $23.9079   $23.91   $23.90   $23.90  
  Purchase #5 $62.94   7.580%   $67.7109   $67.71   $67.70   $67.70  
  Purchase #6 $190.47   13.464%   $216.1149   $216.11   $216.10   $216.10  
  Purchase #7 $67.39   11.382%   $75.0603   $75.06   $75.05   $75.10  
  7 purchase totals = $632.33       $700.4713   $700.47   $700.45   $700.50