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 $84.57   11.236%   $94.0723   $94.07   $94.05   $94.10  
  Purchase #2 $108.88   10.128%   $119.9074   $119.91   $119.90   $119.90  
  Purchase #3 $195.51   9.409%   $213.9055   $213.91   $213.90   $213.90  
  Purchase #4 $242.30   8.570%   $263.0651   $263.07   $263.05   $263.10  
  Purchase #5 $173.56   12.523%   $195.2949   $195.29   $195.30   $195.30  
  Purchase #6 $155.59   9.435%   $170.2699   $170.27   $170.25   $170.30  
  Purchase #7 $222.82   6.304%   $236.8666   $236.87   $236.85   $236.90  
  7 purchase totals = $1,183.23       $1,293.3817   $1,293.39   $1,293.30   $1,293.50