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	$248.37	7.738%	$267.5889	$267.59	$267.60	$267.60
Purchase #2	$167.88	3.332%	$173.4738	$173.47	$173.45	$173.50
Purchase #3	$130.45	9.827%	$143.2693	$143.27	$143.25	$143.30
Purchase #4	$45.31	11.491%	$50.5166	$50.52	$50.50	$50.50
Purchase #5	$144.44	3.498%	$149.4925	$149.49	$149.50	$149.50
Purchase #6	$230.58	11.510%	$257.1198	$257.12	$257.10	$257.10
Purchase #7	$235.38	9.148%	$256.9126	$256.91	$256.90	$256.90
7 purchase totals =	$1,202.41		$1,298.3735	$1,298.37	$1,298.30	$1,298.40