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	$210.53	12.809%	$237.4968	$237.50	$237.50	$237.50
Purchase #2	$61.80	12.486%	$69.5163	$69.52	$69.50	$69.50
Purchase #3	$230.33	3.717%	$238.8914	$238.89	$238.90	$238.90
Purchase #4	$234.47	13.366%	$265.8093	$265.81	$265.80	$265.80
Purchase #5	$172.44	6.388%	$183.4555	$183.46	$183.45	$183.50
Purchase #6	$152.60	3.604%	$158.0997	$158.10	$158.10	$158.10
Purchase #7	$61.29	12.612%	$69.0199	$69.02	$69.00	$69.00
7 purchase totals =	$1,123.46		$1,222.2889	$1,222.30	$1,222.25	$1,222.30