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 $142.56   6.342%   $151.6012   $151.60   $151.60   $151.60  
  Purchase #2 $70.45   8.687%   $76.57   $76.57   $76.55   $76.60  
  Purchase #3 $188.82   8.257%   $204.4109   $204.41   $204.40   $204.40  
  Purchase #4 $88.89   3.468%   $91.9727   $91.97   $91.95   $92.00  
  Purchase #5 $56.61   4.702%   $59.2718   $59.27   $59.25   $59.30  
  Purchase #6 $129.66   12.340%   $145.66   $145.66   $145.65   $145.70  
  Purchase #7 $46.96   8.601%   $50.999   $51.00   $51.00   $51.00  
  7 purchase totals = $723.95       $780.4856   $780.48   $780.40   $780.60