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	$33.87	5.235%	$35.6431	$35.64	$35.65	$35.60
Purchase #2	$231.42	8.388%	$250.8315	$250.83	$250.85	$250.80
Purchase #3	$74.67	7.328%	$80.1418	$80.14	$80.15	$80.10
Purchase #4	$78.85	3.420%	$81.5467	$81.55	$81.55	$81.50
Purchase #5	$35.85	10.176%	$39.4981	$39.50	$39.50	$39.50
Purchase #6	$55.34	4.546%	$57.8558	$57.86	$57.85	$57.90
Purchase #7	$45.50	13.790%	$51.7745	$51.77	$51.75	$51.80
7 purchase totals =	$555.50		$597.2915	$597.29	$597.30	$597.20