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	$27.93	6.323%	$29.696	$29.70	$29.70	$29.70
Purchase #2	$165.89	11.248%	$184.5493	$184.55	$184.55	$184.50
Purchase #3	$80.80	13.458%	$91.6741	$91.67	$91.65	$91.70
Purchase #4	$16.41	10.746%	$18.1734	$18.17	$18.15	$18.20
Purchase #5	$43.72	3.197%	$45.1177	$45.12	$45.10	$45.10
Purchase #6	$246.27	7.406%	$264.5088	$264.51	$264.50	$264.50
Purchase #7	$122.43	4.495%	$127.9332	$127.93	$127.95	$127.90
7 purchase totals =	$703.45		$761.6525	$761.65	$761.60	$761.60