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 $58.86   5.132%   $61.8807   $61.88   $61.90   $61.90  
  Purchase #2 $242.51   7.335%   $260.2981   $260.30   $260.30   $260.30  
  Purchase #3 $143.44   7.486%   $154.1779   $154.18   $154.20   $154.20  
  Purchase #4 $108.81   9.611%   $119.2677   $119.27   $119.25   $119.30  
  Purchase #5 $106.51   11.873%   $119.1559   $119.16   $119.15   $119.20  
  Purchase #6 $194.92   10.509%   $215.4041   $215.40   $215.40   $215.40  
  Purchase #7 $215.94   11.195%   $240.1145   $240.11   $240.10   $240.10  
  7 purchase totals = $1,070.99       $1,170.2989   $1,170.30   $1,170.30   $1,170.40