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	$229.57	13.383%	$260.2934	$260.29	$260.30	$260.30
Purchase #2	$153.87	3.358%	$159.037	$159.04	$159.05	$159.00
Purchase #3	$243.59	4.543%	$254.6563	$254.66	$254.65	$254.70
Purchase #4	$82.70	10.128%	$91.0759	$91.08	$91.10	$91.10
Purchase #5	$91.72	9.189%	$100.1482	$100.15	$100.15	$100.10
Purchase #6	$126.85	11.484%	$141.4175	$141.42	$141.40	$141.40
Purchase #7	$196.61	12.152%	$220.502	$220.50	$220.50	$220.50
7 purchase totals =	$1,124.91		$1,227.1303	$1,227.14	$1,227.15	$1,227.10