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	$20.64	4.191%	$21.505	$21.51	$21.50	$21.50
Purchase #2	$67.56	13.390%	$76.6063	$76.61	$76.60	$76.60
Purchase #3	$84.30	5.148%	$88.6398	$88.64	$88.65	$88.60
Purchase #4	$132.71	6.634%	$141.514	$141.51	$141.50	$141.50
Purchase #5	$81.27	10.182%	$89.5449	$89.54	$89.55	$89.50
Purchase #6	$135.52	11.621%	$151.2688	$151.27	$151.25	$151.30
Purchase #7	$30.41	9.863%	$33.4093	$33.41	$33.40	$33.40
7 purchase totals =	$552.41		$602.4881	$602.49	$602.45	$602.40