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	$243.79	4.619%	$255.0507	$255.05	$255.05	$255.10
Purchase #2	$101.52	8.131%	$109.7746	$109.77	$109.75	$109.80
Purchase #3	$131.93	10.215%	$145.4066	$145.41	$145.40	$145.40
Purchase #4	$223.35	5.128%	$234.8034	$234.80	$234.80	$234.80
Purchase #5	$130.56	6.169%	$138.6142	$138.61	$138.60	$138.60
Purchase #6	$238.75	10.502%	$263.8235	$263.82	$263.80	$263.80
Purchase #7	$66.91	4.389%	$69.8467	$69.85	$69.85	$69.80
7 purchase totals =	$1,136.81		$1,217.3197	$1,217.31	$1,217.25	$1,217.30