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 $56.89   7.105%   $60.932   $60.93   $60.95   $60.90  
  Purchase #2 $42.42   12.585%   $47.7586   $47.76   $47.75   $47.80  
  Purchase #3 $119.97   5.730%   $126.8443   $126.84   $126.85   $126.80  
  Purchase #4 $54.93   5.349%   $57.8682   $57.87   $57.85   $57.90  
  Purchase #5 $218.79   10.151%   $240.9994   $241.00   $241.00   $241.00  
  Purchase #6 $78.69   10.836%   $87.2168   $87.22   $87.20   $87.20  
  Purchase #7 $160.40   12.363%   $180.2303   $180.23   $180.25   $180.20  
  7 purchase totals = $732.09       $801.8496   $801.85   $801.85   $801.80