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	$30.87	5.308%	$32.5086	$32.51	$32.50	$32.50
Purchase #2	$176.72	11.712%	$197.4174	$197.42	$197.40	$197.40
Purchase #3	$160.54	7.857%	$173.1536	$173.15	$173.15	$173.20
Purchase #4	$138.89	7.445%	$149.2304	$149.23	$149.25	$149.20
Purchase #5	$53.72	11.342%	$59.8129	$59.81	$59.80	$59.80
Purchase #6	$71.66	8.597%	$77.8206	$77.82	$77.80	$77.80
Purchase #7	$30.73	5.430%	$32.3986	$32.40	$32.40	$32.40
7 purchase totals =	$663.13		$722.3421	$722.34	$722.30	$722.30