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	$215.99	12.451%	$242.8829	$242.88	$242.90	$242.90
Purchase #2	$99.72	13.841%	$113.5222	$113.52	$113.50	$113.50
Purchase #3	$144.33	10.261%	$159.1397	$159.14	$159.15	$159.10
Purchase #4	$33.62	12.194%	$37.7196	$37.72	$37.70	$37.70
Purchase #5	$120.36	10.628%	$133.1519	$133.15	$133.15	$133.20
Purchase #6	$160.73	7.233%	$172.3556	$172.36	$172.35	$172.40
Purchase #7	$42.86	13.478%	$48.6367	$48.64	$48.65	$48.60
7 purchase totals =	$817.61		$907.4086	$907.41	$907.40	$907.40