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 $87.78   7.644%   $94.4899   $94.49   $94.50   $94.50  
  Purchase #2 $221.99   11.664%   $247.8829   $247.88   $247.90   $247.90  
  Purchase #3 $58.87   7.716%   $63.4124   $63.41   $63.40   $63.40  
  Purchase #4 $213.78   13.407%   $242.4415   $242.44   $242.45   $242.40  
  Purchase #5 $119.98   10.725%   $132.8479   $132.85   $132.85   $132.80  
  Purchase #6 $98.38   4.297%   $102.6074   $102.61   $102.60   $102.60  
  Purchase #7 $170.86   8.541%   $185.4532   $185.45   $185.45   $185.50  
  7 purchase totals = $971.64       $1,069.1352   $1,069.13   $1,069.15   $1,069.10