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 $195.73   6.428%   $208.3115   $208.31   $208.30   $208.30  
  Purchase #2 $84.95   10.411%   $93.7941   $93.79   $93.80   $93.80  
  Purchase #3 $53.73   13.847%   $61.17   $61.17   $61.15   $61.20  
  Purchase #4 $221.42   11.752%   $247.4413   $247.44   $247.45   $247.40  
  Purchase #5 $77.95   13.862%   $88.7554   $88.76   $88.75   $88.80  
  Purchase #6 $15.79   10.717%   $17.4822   $17.48   $17.50   $17.50  
  Purchase #7 $174.80   5.449%   $184.3249   $184.32   $184.30   $184.30  
  7 purchase totals = $824.37       $901.2794   $901.27   $901.25   $901.30