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 $56.91   10.249%   $62.7427   $62.74   $62.75   $62.70  
  Purchase #2 $148.91   3.624%   $154.3065   $154.31   $154.30   $154.30  
  Purchase #3 $69.89   10.473%   $77.2096   $77.21   $77.20   $77.20  
  Purchase #4 $23.74   7.279%   $25.468   $25.47   $25.45   $25.50  
  Purchase #5 $250.27   13.566%   $284.2216   $284.22   $284.20   $284.20  
  Purchase #6 $57.52   8.855%   $62.6134   $62.61   $62.60   $62.60  
  Purchase #7 $139.26   11.851%   $155.7637   $155.76   $155.75   $155.80  
  7 purchase totals = $746.50       $822.3255   $822.32   $822.25   $822.30