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 $60.45   9.414%   $66.1408   $66.14   $66.15   $66.10  
  Purchase #2 $108.76   5.692%   $114.9506   $114.95   $114.95   $115.00  
  Purchase #3 $63.57   8.270%   $68.8272   $68.83   $68.85   $68.80  
  Purchase #4 $185.70   6.166%   $197.1503   $197.15   $197.15   $197.20  
  Purchase #5 $169.34   4.184%   $176.4252   $176.43   $176.45   $176.40  
  Purchase #6 $103.53   8.695%   $112.5319   $112.53   $112.55   $112.50  
  Purchase #7 $67.52   4.374%   $70.4733   $70.47   $70.45   $70.50  
  7 purchase totals = $758.87       $806.4993   $806.50   $806.55   $806.50