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 $110.97   4.416%   $115.8704   $115.87   $115.85   $115.90  
  Purchase #2 $119.97   6.251%   $127.4693   $127.47   $127.45   $127.50  
  Purchase #3 $141.54   12.720%   $159.5439   $159.54   $159.55   $159.50  
  Purchase #4 $24.42   10.682%   $27.0285   $27.03   $27.05   $27.00  
  Purchase #5 $207.90   7.174%   $222.8147   $222.81   $222.80   $222.80  
  Purchase #6 $211.77   10.204%   $233.379   $233.38   $233.40   $233.40  
  Purchase #7 $50.55   6.158%   $53.6629   $53.66   $53.65   $53.70  
  7 purchase totals = $867.12       $939.7687   $939.76   $939.75   $939.80