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 $247.43   5.698%   $261.5286   $261.53   $261.55   $261.50  
  Purchase #2 $14.62   5.676%   $15.4498   $15.45   $15.45   $15.40  
  Purchase #3 $161.36   5.479%   $170.2009   $170.20   $170.20   $170.20  
  Purchase #4 $63.74   10.733%   $70.5812   $70.58   $70.60   $70.60  
  Purchase #5 $70.74   3.817%   $73.4401   $73.44   $73.45   $73.40  
  Purchase #6 $104.91   4.261%   $109.3802   $109.38   $109.40   $109.40  
  Purchase #7 $44.54   11.457%   $49.6429   $49.64   $49.65   $49.60  
  7 purchase totals = $707.34       $750.2237   $750.22   $750.30   $750.10