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 $62.46   11.679%   $69.7547   $69.75   $69.75   $69.80  
  Purchase #2 $244.97   6.147%   $260.0283   $260.03   $260.05   $260.00  
  Purchase #3 $142.51   8.380%   $154.4523   $154.45   $154.45   $154.50  
  Purchase #4 $127.73   12.170%   $143.2747   $143.27   $143.25   $143.30  
  Purchase #5 $219.57   13.688%   $249.6247   $249.62   $249.60   $249.60  
  Purchase #6 $52.54   4.631%   $54.9731   $54.97   $54.95   $55.00  
  Purchase #7 $48.77   8.226%   $52.7818   $52.78   $52.80   $52.80  
  7 purchase totals = $898.55       $984.8896   $984.87   $984.85   $985.00