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 $41.94   9.589%   $45.9616   $45.96   $45.95   $46.00  
  Purchase #2 $29.92   12.233%   $33.5801   $33.58   $33.60   $33.60  
  Purchase #3 $119.61   11.712%   $133.6187   $133.62   $133.60   $133.60  
  Purchase #4 $68.38   5.200%   $71.9358   $71.94   $71.95   $71.90  
  Purchase #5 $213.31   12.378%   $239.7135   $239.71   $239.70   $239.70  
  Purchase #6 $234.31   11.808%   $261.9773   $261.98   $262.00   $262.00  
  Purchase #7 $13.88   10.784%   $15.3768   $15.38   $15.40   $15.40  
  7 purchase totals = $721.35       $802.1638   $802.17   $802.20   $802.20