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 $207.93   3.196%   $214.5754   $214.58   $214.60   $214.60  
  Purchase #2 $104.82   13.302%   $118.7632   $118.76   $118.75   $118.80  
  Purchase #3 $148.46   10.474%   $164.0097   $164.01   $164.00   $164.00  
  Purchase #4 $116.39   7.548%   $125.1751   $125.18   $125.20   $125.20  
  Purchase #5 $82.53   5.440%   $87.0196   $87.02   $87.00   $87.00  
  Purchase #6 $50.87   3.141%   $52.4678   $52.47   $52.45   $52.50  
  Purchase #7 $210.79   6.495%   $224.4808   $224.48   $224.50   $224.50  
  7 purchase totals = $921.79       $986.4916   $986.50   $986.50   $986.60