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	$225.28	13.608%	$255.9361	$255.94	$255.95	$255.90
Purchase #2	$150.44	3.778%	$156.1236	$156.12	$156.10	$156.10
Purchase #3	$122.73	4.142%	$127.8135	$127.81	$127.80	$127.80
Purchase #4	$247.96	8.545%	$269.1482	$269.15	$269.15	$269.10
Purchase #5	$194.88	4.340%	$203.3378	$203.34	$203.35	$203.30
Purchase #6	$80.68	9.597%	$88.4229	$88.42	$88.40	$88.40
Purchase #7	$124.40	6.849%	$132.9202	$132.92	$132.90	$132.90
7 purchase totals =	$1,146.37		$1,233.7023	$1,233.70	$1,233.65	$1,233.50