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 $83.82   11.465%   $93.43   $93.43   $93.45   $93.40  
  Purchase #2 $33.35   4.706%   $34.9195   $34.92   $34.90   $34.90  
  Purchase #3 $96.66   10.859%   $107.1563   $107.16   $107.15   $107.20  
  Purchase #4 $51.27   8.372%   $55.5623   $55.56   $55.55   $55.60  
  Purchase #5 $228.96   12.365%   $257.2709   $257.27   $257.25   $257.30  
  Purchase #6 $161.90   6.365%   $172.2049   $172.20   $172.20   $172.20  
  Purchase #7 $213.68   8.160%   $231.1163   $231.12   $231.10   $231.10  
  7 purchase totals = $869.64       $951.6602   $951.66   $951.60   $951.70