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	$16.72	9.118%	$18.2445	$18.24	$18.25	$18.20
Purchase #2	$26.74	10.300%	$29.4942	$29.49	$29.50	$29.50
Purchase #3	$77.88	13.472%	$88.372	$88.37	$88.35	$88.40
Purchase #4	$58.52	10.196%	$64.4867	$64.49	$64.50	$64.50
Purchase #5	$164.49	5.627%	$173.7459	$173.75	$173.75	$173.70
Purchase #6	$133.58	12.641%	$150.4658	$150.47	$150.45	$150.50
Purchase #7	$50.90	6.694%	$54.3072	$54.31	$54.30	$54.30
7 purchase totals =	$528.83		$579.1163	$579.12	$579.10	$579.10