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 $85.65   12.361%   $96.2372   $96.24   $96.25   $96.20  
  Purchase #2 $17.97   12.604%   $20.2349   $20.23   $20.25   $20.20  
  Purchase #3 $58.96   7.755%   $63.5323   $63.53   $63.55   $63.50  
  Purchase #4 $245.59   3.384%   $253.9008   $253.90   $253.90   $253.90  
  Purchase #5 $236.37   3.312%   $244.1986   $244.20   $244.20   $244.20  
  Purchase #6 $137.70   8.205%   $148.9983   $149.00   $149.00   $149.00  
  Purchase #7 $157.47   7.376%   $169.085   $169.09   $169.10   $169.10  
  7 purchase totals = $939.71       $996.1871   $996.19   $996.25   $996.10