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 $112.44   13.269%   $127.3597   $127.36   $127.35   $127.40  
  Purchase #2 $13.56   6.105%   $14.3878   $14.39   $14.40   $14.40  
  Purchase #3 $96.69   3.672%   $100.2405   $100.24   $100.25   $100.20  
  Purchase #4 $85.39   9.502%   $93.5038   $93.50   $93.50   $93.50  
  Purchase #5 $25.50   7.356%   $27.3758   $27.38   $27.40   $27.40  
  Purchase #6 $63.68   6.568%   $67.8625   $67.86   $67.85   $67.90  
  Purchase #7 $184.68   4.611%   $193.1956   $193.20   $193.20   $193.20  
  7 purchase totals = $581.94       $623.9257   $623.93   $623.95   $624.00