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 $92.55   13.185%   $104.7527   $104.75   $104.75   $104.80  
  Purchase #2 $194.36   9.348%   $212.5288   $212.53   $212.55   $212.50  
  Purchase #3 $115.58   10.567%   $127.7933   $127.79   $127.80   $127.80  
  Purchase #4 $166.61   6.181%   $176.9082   $176.91   $176.90   $176.90  
  Purchase #5 $15.63   3.507%   $16.1781   $16.18   $16.20   $16.20  
  Purchase #6 $157.34   8.207%   $170.2529   $170.25   $170.25   $170.30  
  Purchase #7 $55.58   7.269%   $59.6201   $59.62   $59.60   $59.60  
  7 purchase totals = $797.65       $868.0341   $868.03   $868.05   $868.10