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	$44.68	7.721%	$48.1297	$48.13	$48.15	$48.10
Purchase #2	$139.31	11.156%	$154.8514	$154.85	$154.85	$154.90
Purchase #3	$41.86	11.693%	$46.7547	$46.75	$46.75	$46.80
Purchase #4	$12.59	13.459%	$14.2845	$14.28	$14.30	$14.30
Purchase #5	$156.72	10.215%	$172.7289	$172.73	$172.75	$172.70
Purchase #6	$92.55	9.676%	$101.5051	$101.51	$101.50	$101.50
Purchase #7	$41.50	9.633%	$45.4977	$45.50	$45.50	$45.50
7 purchase totals =	$529.21		$583.7520	$583.75	$583.80	$583.80