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 $224.97   8.481%   $244.0497   $244.05   $244.05   $244.00  
  Purchase #2 $117.70   7.103%   $126.0602   $126.06   $126.05   $126.10  
  Purchase #3 $91.79   6.823%   $98.0528   $98.05   $98.05   $98.10  
  Purchase #4 $44.68   9.863%   $49.0868   $49.09   $49.10   $49.10  
  Purchase #5 $226.82   12.746%   $255.7305   $255.73   $255.75   $255.70  
  Purchase #6 $143.51   10.533%   $158.6259   $158.63   $158.65   $158.60  
  Purchase #7 $36.77   7.150%   $39.3991   $39.40   $39.40   $39.40  
  7 purchase totals = $886.24       $971.0050   $971.01   $971.05   $971.00