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	$60.59	10.224%	$66.7847	$66.78	$66.80	$66.80
Purchase #2	$218.28	13.407%	$247.5448	$247.54	$247.55	$247.50
Purchase #3	$78.75	12.239%	$88.3882	$88.39	$88.40	$88.40
Purchase #4	$151.96	4.309%	$158.508	$158.51	$158.50	$158.50
Purchase #5	$133.54	7.525%	$143.5889	$143.59	$143.60	$143.60
Purchase #6	$64.77	12.293%	$72.7322	$72.73	$72.75	$72.70
Purchase #7	$171.35	5.127%	$180.1351	$180.14	$180.15	$180.10
7 purchase totals =	$879.24		$957.6819	$957.68	$957.75	$957.60