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	$12.31	8.633%	$13.3727	$13.37	$13.35	$13.40
Purchase #2	$93.68	12.737%	$105.612	$105.61	$105.60	$105.60
Purchase #3	$216.74	5.845%	$229.4085	$229.41	$229.40	$229.40
Purchase #4	$89.88	6.740%	$95.9379	$95.94	$95.95	$95.90
Purchase #5	$64.88	3.422%	$67.1002	$67.10	$67.10	$67.10
Purchase #6	$77.65	4.607%	$81.2273	$81.23	$81.25	$81.20
Purchase #7	$140.32	4.482%	$146.6091	$146.61	$146.60	$146.60
7 purchase totals =	$695.46		$739.2677	$739.27	$739.25	$739.20