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	$45.91	6.117%	$48.7183	$48.72	$48.70	$48.70
Purchase #2	$196.36	3.805%	$203.8315	$203.83	$203.85	$203.80
Purchase #3	$216.83	6.194%	$230.2605	$230.26	$230.25	$230.30
Purchase #4	$164.70	11.829%	$184.1824	$184.18	$184.20	$184.20
Purchase #5	$90.27	3.677%	$93.5892	$93.59	$93.60	$93.60
Purchase #6	$179.52	6.478%	$191.1493	$191.15	$191.15	$191.10
Purchase #7	$109.60	12.659%	$123.4743	$123.47	$123.45	$123.50
7 purchase totals =	$1,003.19		$1,075.2055	$1,075.20	$1,075.20	$1,075.20