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 $119.27   5.639%   $125.9956   $126.00   $126.00   $126.00  
  Purchase #2 $82.61   7.631%   $88.914   $88.91   $88.90   $88.90  
  Purchase #3 $69.29   13.335%   $78.5298   $78.53   $78.55   $78.50  
  Purchase #4 $183.28   13.439%   $207.911   $207.91   $207.90   $207.90  
  Purchase #5 $28.80   3.304%   $29.7516   $29.75   $29.75   $29.80  
  Purchase #6 $72.38   13.451%   $82.1158   $82.12   $82.10   $82.10  
  Purchase #7 $128.34   13.750%   $145.9868   $145.99   $146.00   $146.00  
  7 purchase totals = $683.97       $759.2046   $759.21   $759.20   $759.20