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	$37.69	7.508%	$40.5198	$40.52	$40.50	$40.50
Purchase #2	$6.91	9.417%	$7.5607	$7.56	$7.55	$7.60
Purchase #3	$162.61	13.181%	$184.0436	$184.04	$184.05	$184.00
Purchase #4	$205.58	12.260%	$230.7841	$230.78	$230.80	$230.80
Purchase #5	$56.75	10.412%	$62.6588	$62.66	$62.65	$62.70
Purchase #6	$152.70	5.394%	$160.9366	$160.94	$160.95	$160.90
Purchase #7	$119.64	6.605%	$127.5422	$127.54	$127.55	$127.50
7 purchase totals =	$741.88		$814.0458	$814.04	$814.05	$814.00