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 $118.73   6.109%   $125.9832   $125.98   $126.00   $126.00  
  Purchase #2 $113.94   13.127%   $128.8969   $128.90   $128.90   $128.90  
  Purchase #3 $171.49   10.634%   $189.7262   $189.73   $189.75   $189.70  
  Purchase #4 $154.95   3.285%   $160.0401   $160.04   $160.05   $160.00  
  Purchase #5 $148.38   7.106%   $158.9239   $158.92   $158.90   $158.90  
  Purchase #6 $153.92   4.783%   $161.282   $161.28   $161.30   $161.30  
  Purchase #7 $226.27   5.389%   $238.4637   $238.46   $238.45   $238.50  
  7 purchase totals = $1,087.68       $1,163.3160   $1,163.31   $1,163.35   $1,163.30