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 $46.71   8.468%   $50.6654   $50.67   $50.65   $50.70  
  Purchase #2 $62.25   11.824%   $69.6104   $69.61   $69.60   $69.60  
  Purchase #3 $21.75   11.160%   $24.1773   $24.18   $24.20   $24.20  
  Purchase #4 $230.58   3.690%   $239.0884   $239.09   $239.10   $239.10  
  Purchase #5 $242.63   9.231%   $265.0272   $265.03   $265.05   $265.00  
  Purchase #6 $99.98   12.233%   $112.2106   $112.21   $112.20   $112.20  
  Purchase #7 $50.89   6.778%   $54.3393   $54.34   $54.35   $54.30  
  7 purchase totals = $754.79       $815.1186   $815.13   $815.15   $815.10