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 $56.74   8.673%   $61.6611   $61.66   $61.65   $61.70  
  Purchase #2 $174.37   8.548%   $189.2751   $189.28   $189.30   $189.30  
  Purchase #3 $186.65   4.473%   $194.9989   $195.00   $195.00   $195.00  
  Purchase #4 $35.48   8.310%   $38.4284   $38.43   $38.45   $38.40  
  Purchase #5 $231.63   12.660%   $260.9544   $260.95   $260.95   $261.00  
  Purchase #6 $48.97   5.717%   $51.7696   $51.77   $51.75   $51.80  
  Purchase #7 $127.41   3.869%   $132.3395   $132.34   $132.35   $132.30  
  7 purchase totals = $861.25       $929.4270   $929.43   $929.45   $929.50