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	$37.92	10.773%	$42.0051	$42.01	$42.00	$42.00
Purchase #2	$91.68	11.388%	$102.1205	$102.12	$102.10	$102.10
Purchase #3	$119.42	6.442%	$127.113	$127.11	$127.10	$127.10
Purchase #4	$119.53	10.867%	$132.5193	$132.52	$132.50	$132.50
Purchase #5	$14.81	4.686%	$15.504	$15.50	$15.50	$15.50
Purchase #6	$77.75	3.140%	$80.1914	$80.19	$80.20	$80.20
Purchase #7	$244.43	11.821%	$273.3241	$273.32	$273.30	$273.30
7 purchase totals =	$705.54		$772.7774	$772.77	$772.70	$772.70