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	$124.98	7.594%	$134.471	$134.47	$134.45	$134.50
Purchase #2	$81.29	5.510%	$85.7691	$85.77	$85.75	$85.80
Purchase #3	$116.30	13.699%	$132.2319	$132.23	$132.25	$132.20
Purchase #4	$49.60	4.346%	$51.7556	$51.76	$51.75	$51.80
Purchase #5	$21.41	3.346%	$22.1264	$22.13	$22.15	$22.10
Purchase #6	$68.55	3.669%	$71.0651	$71.07	$71.05	$71.10
Purchase #7	$38.88	4.759%	$40.7303	$40.73	$40.75	$40.70
7 purchase totals =	$501.01		$538.1494	$538.16	$538.15	$538.20