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	$38.26	5.349%	$40.3065	$40.31	$40.30	$40.30
Purchase #2	$16.48	12.702%	$18.5733	$18.57	$18.55	$18.60
Purchase #3	$156.96	3.172%	$161.9388	$161.94	$161.95	$161.90
Purchase #4	$197.53	9.738%	$216.7655	$216.77	$216.75	$216.80
Purchase #5	$120.25	13.696%	$136.7194	$136.72	$136.70	$136.70
Purchase #6	$129.34	7.757%	$139.3729	$139.37	$139.35	$139.40
Purchase #7	$98.28	13.552%	$111.5989	$111.60	$111.60	$111.60
7 purchase totals =	$757.10		$825.2753	$825.28	$825.20	$825.30