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	$26.50	12.265%	$29.7502	$29.75	$29.75	$29.80
Purchase #2	$140.72	6.857%	$150.3692	$150.37	$150.35	$150.40
Purchase #3	$154.93	11.309%	$172.451	$172.45	$172.45	$172.50
Purchase #4	$51.31	11.771%	$57.3497	$57.35	$57.35	$57.30
Purchase #5	$230.56	9.764%	$253.0719	$253.07	$253.05	$253.10
Purchase #6	$181.93	13.132%	$205.821	$205.82	$205.80	$205.80
Purchase #7	$221.52	10.130%	$243.96	$243.96	$243.95	$244.00
7 purchase totals =	$1,007.47		$1,112.7730	$1,112.77	$1,112.70	$1,112.90