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	$50.81	12.441%	$57.1313	$57.13	$57.15	$57.10
Purchase #2	$223.40	5.145%	$234.8939	$234.89	$234.90	$234.90
Purchase #3	$129.55	13.417%	$146.9317	$146.93	$146.95	$146.90
Purchase #4	$205.91	10.116%	$226.7399	$226.74	$226.75	$226.70
Purchase #5	$141.55	4.784%	$148.3218	$148.32	$148.30	$148.30
Purchase #6	$192.83	10.186%	$212.4717	$212.47	$212.45	$212.50
Purchase #7	$50.27	3.457%	$52.0078	$52.01	$52.00	$52.00
7 purchase totals =	$994.32		$1,078.4981	$1,078.49	$1,078.50	$1,078.40