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 $47.95   7.589%   $51.5889   $51.59   $51.60   $51.60  
  Purchase #2 $70.43   12.201%   $79.0232   $79.02   $79.00   $79.00  
  Purchase #3 $250.97   10.799%   $278.0723   $278.07   $278.05   $278.10  
  Purchase #4 $88.41   8.850%   $96.2343   $96.23   $96.25   $96.20  
  Purchase #5 $229.95   6.196%   $244.1977   $244.20   $244.20   $244.20  
  Purchase #6 $69.36   12.399%   $77.9599   $77.96   $77.95   $78.00  
  Purchase #7 $197.41   8.689%   $214.563   $214.56   $214.55   $214.60  
  7 purchase totals = $954.48       $1,041.6393   $1,041.63   $1,041.60   $1,041.70