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 $21.61   13.642%   $24.558   $24.56   $24.55   $24.60  
  Purchase #2 $54.79   6.750%   $58.4883   $58.49   $58.50   $58.50  
  Purchase #3 $47.85   8.287%   $51.8153   $51.82   $51.80   $51.80  
  Purchase #4 $129.81   12.399%   $145.9051   $145.91   $145.90   $145.90  
  Purchase #5 $170.76   3.827%   $177.295   $177.30   $177.30   $177.30  
  Purchase #6 $141.76   12.183%   $159.0306   $159.03   $159.05   $159.00  
  Purchase #7 $227.76   12.752%   $256.804   $256.80   $256.80   $256.80  
  7 purchase totals = $794.34       $873.8963   $873.91   $873.90   $873.90