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 $168.89   9.138%   $184.3232   $184.32   $184.30   $184.30  
  Purchase #2 $69.61   9.410%   $76.1603   $76.16   $76.15   $76.20  
  Purchase #3 $46.32   11.192%   $51.5041   $51.50   $51.50   $51.50  
  Purchase #4 $199.44   9.178%   $217.7446   $217.74   $217.75   $217.70  
  Purchase #5 $131.81   12.613%   $148.4352   $148.44   $148.45   $148.40  
  Purchase #6 $60.87   4.459%   $63.5842   $63.58   $63.60   $63.60  
  Purchase #7 $243.30   11.531%   $271.3549   $271.35   $271.35   $271.40  
  7 purchase totals = $920.24       $1,013.1065   $1,013.09   $1,013.10   $1,013.10