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 $194.38   6.584%   $207.178   $207.18   $207.20   $207.20  
  Purchase #2 $116.48   5.542%   $122.9353   $122.94   $122.95   $122.90  
  Purchase #3 $245.33   6.565%   $261.4359   $261.44   $261.45   $261.40  
  Purchase #4 $126.52   8.752%   $137.593   $137.59   $137.60   $137.60  
  Purchase #5 $106.75   8.183%   $115.4854   $115.49   $115.50   $115.50  
  Purchase #6 $52.95   11.614%   $59.0996   $59.10   $59.10   $59.10  
  Purchase #7 $27.30   9.457%   $29.8818   $29.88   $29.90   $29.90  
  7 purchase totals = $869.71       $933.6090   $933.62   $933.70   $933.60