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 $248.90   10.606%   $275.2983   $275.30   $275.30   $275.30  
  Purchase #2 $59.99   7.656%   $64.5828   $64.58   $64.60   $64.60  
  Purchase #3 $166.38   6.671%   $177.4792   $177.48   $177.50   $177.50  
  Purchase #4 $169.75   11.410%   $189.1185   $189.12   $189.10   $189.10  
  Purchase #5 $215.58   6.785%   $230.2071   $230.21   $230.20   $230.20  
  Purchase #6 $189.41   4.473%   $197.8823   $197.88   $197.90   $197.90  
  Purchase #7 $233.87   10.852%   $259.2496   $259.25   $259.25   $259.20  
  7 purchase totals = $1,283.88       $1,393.8178   $1,393.82   $1,393.85   $1,393.80