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 $49.62   5.451%   $52.3248   $52.32   $52.30   $52.30  
  Purchase #2 $73.46   13.371%   $83.2823   $83.28   $83.30   $83.30  
  Purchase #3 $34.49   4.738%   $36.1241   $36.12   $36.10   $36.10  
  Purchase #4 $170.63   8.711%   $185.4936   $185.49   $185.50   $185.50  
  Purchase #5 $219.64   6.221%   $233.3038   $233.30   $233.30   $233.30  
  Purchase #6 $213.91   5.137%   $224.8986   $224.90   $224.90   $224.90  
  Purchase #7 $109.64   8.205%   $118.636   $118.64   $118.65   $118.60  
  7 purchase totals = $871.39       $934.0632   $934.05   $934.05   $934.00