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 $38.46   6.485%   $40.9541   $40.95   $40.95   $41.00  
  Purchase #2 $208.50   9.329%   $227.951   $227.95   $227.95   $228.00  
  Purchase #3 $209.58   11.497%   $233.6754   $233.68   $233.70   $233.70  
  Purchase #4 $33.60   4.347%   $35.0606   $35.06   $35.05   $35.10  
  Purchase #5 $184.78   5.480%   $194.9059   $194.91   $194.90   $194.90  
  Purchase #6 $119.95   10.231%   $132.2221   $132.22   $132.20   $132.20  
  Purchase #7 $140.86   13.193%   $159.4437   $159.44   $159.45   $159.40  
  7 purchase totals = $935.73       $1,024.2128   $1,024.21   $1,024.20   $1,024.30