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 $39.81   11.294%   $44.3061   $44.31   $44.30   $44.30  
  Purchase #2 $104.76   9.103%   $114.2963   $114.30   $114.30   $114.30  
  Purchase #3 $158.91   9.548%   $174.0827   $174.08   $174.10   $174.10  
  Purchase #4 $201.85   7.157%   $216.2964   $216.30   $216.30   $216.30  
  Purchase #5 $6.61   5.853%   $6.9969   $7.00   $7.00   $7.00  
  Purchase #6 $230.71   8.202%   $249.6328   $249.63   $249.65   $249.60  
  Purchase #7 $82.40   12.468%   $92.6736   $92.67   $92.65   $92.70  
  7 purchase totals = $825.05       $898.2848   $898.29   $898.30   $898.30