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	$78.92	4.421%	$82.4091	$82.41	$82.40	$82.40
Purchase #2	$132.94	12.455%	$149.4977	$149.50	$149.50	$149.50
Purchase #3	$143.45	10.191%	$158.069	$158.07	$158.05	$158.10
Purchase #4	$134.95	7.870%	$145.5706	$145.57	$145.55	$145.60
Purchase #5	$194.30	10.195%	$214.1089	$214.11	$214.10	$214.10
Purchase #6	$108.51	13.811%	$123.4963	$123.50	$123.50	$123.50
Purchase #7	$5.78	13.573%	$6.5645	$6.56	$6.55	$6.60
7 purchase totals =	$798.85		$879.7161	$879.72	$879.65	$879.80