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	$49.71	13.677%	$56.5088	$56.51	$56.50	$56.50
Purchase #2	$56.42	6.167%	$59.8994	$59.90	$59.90	$59.90
Purchase #3	$76.72	3.501%	$79.406	$79.41	$79.40	$79.40
Purchase #4	$221.74	5.161%	$233.184	$233.18	$233.20	$233.20
Purchase #5	$122.54	6.309%	$130.271	$130.27	$130.25	$130.30
Purchase #6	$19.47	5.873%	$20.6135	$20.61	$20.60	$20.60
Purchase #7	$21.44	6.754%	$22.8881	$22.89	$22.90	$22.90
7 purchase totals =	$568.04		$602.7708	$602.77	$602.75	$602.80