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 $48.69   8.344%   $52.7527   $52.75   $52.75   $52.80  
  Purchase #2 $222.53   10.282%   $245.4105   $245.41   $245.40   $245.40  
  Purchase #3 $164.96   7.262%   $176.9394   $176.94   $176.95   $176.90  
  Purchase #4 $91.36   7.494%   $98.2065   $98.21   $98.20   $98.20  
  Purchase #5 $94.59   3.647%   $98.0397   $98.04   $98.05   $98.00  
  Purchase #6 $137.60   9.669%   $150.9045   $150.90   $150.90   $150.90  
  Purchase #7 $247.50   4.759%   $259.2785   $259.28   $259.30   $259.30  
  7 purchase totals = $1,007.23       $1,081.5318   $1,081.53   $1,081.55   $1,081.50