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 $216.96   9.758%   $238.131   $238.13   $238.15   $238.10  
  Purchase #2 $126.26   7.827%   $136.1424   $136.14   $136.15   $136.10  
  Purchase #3 $109.63   3.226%   $113.1667   $113.17   $113.15   $113.20  
  Purchase #4 $53.96   11.268%   $60.0402   $60.04   $60.05   $60.00  
  Purchase #5 $156.71   7.853%   $169.0164   $169.02   $169.00   $169.00  
  Purchase #6 $79.42   3.617%   $82.2926   $82.29   $82.30   $82.30  
  Purchase #7 $151.75   6.312%   $161.3285   $161.33   $161.35   $161.30  
  7 purchase totals = $894.69       $960.1178   $960.12   $960.15   $960.00