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 $111.25   13.554%   $126.3288   $126.33   $126.35   $126.30  
  Purchase #2 $234.92   3.381%   $242.8626   $242.86   $242.85   $242.90  
  Purchase #3 $152.34   12.602%   $171.5379   $171.54   $171.55   $171.50  
  Purchase #4 $13.73   13.470%   $15.5794   $15.58   $15.60   $15.60  
  Purchase #5 $102.40   11.325%   $113.9968   $114.00   $114.00   $114.00  
  Purchase #6 $141.59   11.583%   $157.9904   $157.99   $158.00   $158.00  
  Purchase #7 $26.62   9.488%   $29.1457   $29.15   $29.15   $29.10  
  7 purchase totals = $782.85       $857.4416   $857.45   $857.50   $857.40