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	$159.69	8.690%	$173.5671	$173.57	$173.55	$173.60
Purchase #2	$38.45	5.272%	$40.4771	$40.48	$40.50	$40.50
Purchase #3	$126.28	4.161%	$131.5345	$131.53	$131.55	$131.50
Purchase #4	$30.74	7.864%	$33.1574	$33.16	$33.15	$33.20
Purchase #5	$214.42	3.260%	$221.4101	$221.41	$221.40	$221.40
Purchase #6	$37.55	6.437%	$39.9671	$39.97	$39.95	$40.00
Purchase #7	$57.58	8.312%	$62.366	$62.37	$62.35	$62.40
7 purchase totals =	$664.71		$702.4793	$702.49	$702.45	$702.60