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 $111.85   6.105%   $118.6784   $118.68   $118.70   $118.70  
  Purchase #2 $5.54   12.169%   $6.2142   $6.21   $6.20   $6.20  
  Purchase #3 $50.76   13.837%   $57.7837   $57.78   $57.80   $57.80  
  Purchase #4 $25.72   13.114%   $29.0929   $29.09   $29.10   $29.10  
  Purchase #5 $102.32   11.198%   $113.7778   $113.78   $113.80   $113.80  
  Purchase #6 $210.73   10.571%   $233.0063   $233.01   $233.00   $233.00  
  Purchase #7 $247.65   7.663%   $266.6274   $266.63   $266.65   $266.60  
  7 purchase totals = $754.57       $825.1807   $825.18   $825.25   $825.20