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 $230.71   12.533%   $259.6249   $259.62   $259.60   $259.60  
  Purchase #2 $244.82   5.640%   $258.6278   $258.63   $258.65   $258.60  
  Purchase #3 $92.52   13.137%   $104.6744   $104.67   $104.65   $104.70  
  Purchase #4 $176.74   10.871%   $195.9534   $195.95   $195.95   $196.00  
  Purchase #5 $151.67   4.635%   $158.6999   $158.70   $158.70   $158.70  
  Purchase #6 $233.64   11.832%   $261.2843   $261.28   $261.30   $261.30  
  Purchase #7 $216.34   7.548%   $232.6693   $232.67   $232.65   $232.70  
  7 purchase totals = $1,346.44       $1,471.5340   $1,471.52   $1,471.50   $1,471.60