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 $136.43   3.569%   $141.2992   $141.30   $141.30   $141.30  
  Purchase #2 $59.63   11.270%   $66.3503   $66.35   $66.35   $66.40  
  Purchase #3 $78.85   8.737%   $85.7391   $85.74   $85.75   $85.70  
  Purchase #4 $28.26   5.781%   $29.8937   $29.89   $29.90   $29.90  
  Purchase #5 $244.75   9.601%   $268.2484   $268.25   $268.25   $268.20  
  Purchase #6 $126.93   4.781%   $132.9985   $133.00   $133.00   $133.00  
  Purchase #7 $161.73   9.325%   $176.8113   $176.81   $176.80   $176.80  
  7 purchase totals = $836.58       $901.3405   $901.34   $901.35   $901.30