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 $88.40   11.734%   $98.7729   $98.77   $98.75   $98.80  
  Purchase #2 $178.55   9.243%   $195.0534   $195.05   $195.05   $195.10  
  Purchase #3 $84.76   11.736%   $94.7074   $94.71   $94.70   $94.70  
  Purchase #4 $250.86   5.379%   $264.3538   $264.35   $264.35   $264.40  
  Purchase #5 $111.72   11.108%   $124.1299   $124.13   $124.15   $124.10  
  Purchase #6 $159.65   7.387%   $171.4433   $171.44   $171.45   $171.40  
  Purchase #7 $19.30   11.248%   $21.4709   $21.47   $21.45   $21.50  
  7 purchase totals = $893.24       $969.9316   $969.92   $969.90   $970.00