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 $7.96   3.617%   $8.2479   $8.25   $8.25   $8.20  
  Purchase #2 $242.84   7.117%   $260.1229   $260.12   $260.10   $260.10  
  Purchase #3 $53.85   11.342%   $59.9577   $59.96   $59.95   $60.00  
  Purchase #4 $174.89   6.514%   $186.2823   $186.28   $186.30   $186.30  
  Purchase #5 $116.83   11.213%   $129.9301   $129.93   $129.95   $129.90  
  Purchase #6 $197.54   12.151%   $221.5431   $221.54   $221.55   $221.50  
  Purchase #7 $239.63   3.603%   $248.2639   $248.26   $248.25   $248.30  
  7 purchase totals = $1,033.54       $1,114.3479   $1,114.34   $1,114.35   $1,114.30