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	$155.29	13.773%	$176.6781	$176.68	$176.70	$176.70
Purchase #2	$242.50	5.145%	$254.9766	$254.98	$255.00	$255.00
Purchase #3	$107.38	4.543%	$112.2583	$112.26	$112.25	$112.30
Purchase #4	$50.41	5.668%	$53.2672	$53.27	$53.25	$53.30
Purchase #5	$179.53	5.140%	$188.7578	$188.76	$188.75	$188.80
Purchase #6	$7.27	5.494%	$7.6694	$7.67	$7.65	$7.70
Purchase #7	$99.86	3.863%	$103.7176	$103.72	$103.70	$103.70
7 purchase totals =	$842.24		$897.3250	$897.34	$897.30	$897.50