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 $199.98   8.519%   $217.0163   $217.02   $217.00   $217.00  
  Purchase #2 $94.90   8.625%   $103.0851   $103.09   $103.10   $103.10  
  Purchase #3 $72.94   4.528%   $76.2427   $76.24   $76.25   $76.20  
  Purchase #4 $138.54   11.583%   $154.5871   $154.59   $154.60   $154.60  
  Purchase #5 $211.57   10.455%   $233.6896   $233.69   $233.70   $233.70  
  Purchase #6 $22.89   6.845%   $24.4568   $24.46   $24.45   $24.50  
  Purchase #7 $226.87   11.741%   $253.5068   $253.51   $253.50   $253.50  
  7 purchase totals = $967.69       $1,062.5844   $1,062.60   $1,062.60   $1,062.60