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 $109.81   3.852%   $114.0399   $114.04   $114.05   $114.00  
  Purchase #2 $221.84   12.134%   $248.7581   $248.76   $248.75   $248.80  
  Purchase #3 $158.91   7.592%   $170.9744   $170.97   $170.95   $171.00  
  Purchase #4 $246.32   9.354%   $269.3608   $269.36   $269.35   $269.40  
  Purchase #5 $54.41   8.501%   $59.0354   $59.04   $59.05   $59.00  
  Purchase #6 $51.47   9.452%   $56.3349   $56.33   $56.35   $56.30  
  Purchase #7 $52.70   9.554%   $57.735   $57.74   $57.75   $57.70  
  7 purchase totals = $895.46       $976.2385   $976.24   $976.25   $976.20