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 $33.83   4.757%   $35.4393   $35.44   $35.45   $35.40  
  Purchase #2 $247.58   3.485%   $256.2082   $256.21   $256.20   $256.20  
  Purchase #3 $118.70   11.533%   $132.3897   $132.39   $132.40   $132.40  
  Purchase #4 $212.41   7.193%   $227.6887   $227.69   $227.70   $227.70  
  Purchase #5 $54.93   6.269%   $58.3736   $58.37   $58.35   $58.40  
  Purchase #6 $43.78   5.809%   $46.3232   $46.32   $46.30   $46.30  
  Purchase #7 $199.77   3.162%   $206.0867   $206.09   $206.10   $206.10  
  7 purchase totals = $911.00       $962.5094   $962.51   $962.50   $962.50