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 $115.67   11.704%   $129.208   $129.21   $129.20   $129.20  
  Purchase #2 $164.48   11.295%   $183.058   $183.06   $183.05   $183.10  
  Purchase #3 $193.70   8.766%   $210.6797   $210.68   $210.70   $210.70  
  Purchase #4 $38.97   11.200%   $43.3346   $43.33   $43.35   $43.30  
  Purchase #5 $64.82   6.824%   $69.2433   $69.24   $69.25   $69.20  
  Purchase #6 $69.41   8.185%   $75.0912   $75.09   $75.10   $75.10  
  Purchase #7 $217.53   12.749%   $245.2629   $245.26   $245.25   $245.30  
  7 purchase totals = $864.58       $955.8777   $955.87   $955.90   $955.90