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 $90.87   8.228%   $98.3468   $98.35   $98.35   $98.30  
  Purchase #2 $243.36   10.443%   $268.7741   $268.77   $268.75   $268.80  
  Purchase #3 $231.49   10.851%   $256.609   $256.61   $256.60   $256.60  
  Purchase #4 $129.76   4.198%   $135.2073   $135.21   $135.20   $135.20  
  Purchase #5 $107.97   13.246%   $122.2717   $122.27   $122.25   $122.30  
  Purchase #6 $14.46   4.631%   $15.1296   $15.13   $15.15   $15.10  
  Purchase #7 $64.79   3.351%   $66.9611   $66.96   $66.95   $67.00  
  7 purchase totals = $882.70       $963.2996   $963.30   $963.25   $963.30