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	$5.70	8.813%	$6.2023	$6.20	$6.20	$6.20
Purchase #2	$78.99	12.461%	$88.8329	$88.83	$88.85	$88.80
Purchase #3	$98.93	12.418%	$111.2151	$111.22	$111.20	$111.20
Purchase #4	$244.96	4.390%	$255.7137	$255.71	$255.70	$255.70
Purchase #5	$132.82	10.562%	$146.8484	$146.85	$146.85	$146.80
Purchase #6	$123.38	8.319%	$133.644	$133.64	$133.65	$133.60
Purchase #7	$33.53	13.668%	$38.1129	$38.11	$38.10	$38.10
7 purchase totals =	$718.31		$780.5693	$780.56	$780.55	$780.40