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 $36.63   11.868%   $40.9772   $40.98   $41.00   $41.00  
  Purchase #2 $175.40   9.267%   $191.6543   $191.65   $191.65   $191.70  
  Purchase #3 $104.73   11.821%   $117.1101   $117.11   $117.10   $117.10  
  Purchase #4 $16.84   13.131%   $19.0513   $19.05   $19.05   $19.10  
  Purchase #5 $69.39   5.291%   $73.0614   $73.06   $73.05   $73.10  
  Purchase #6 $239.62   6.464%   $255.109   $255.11   $255.10   $255.10  
  Purchase #7 $191.79   7.565%   $206.2989   $206.30   $206.30   $206.30  
  7 purchase totals = $834.40       $903.2622   $903.26   $903.25   $903.40