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	$225.73	13.683%	$256.6166	$256.62	$256.60	$256.60
Purchase #2	$243.48	11.419%	$271.283	$271.28	$271.30	$271.30
Purchase #3	$86.32	12.569%	$97.1696	$97.17	$97.15	$97.20
Purchase #4	$11.75	11.731%	$13.1284	$13.13	$13.15	$13.10
Purchase #5	$161.44	10.366%	$178.1749	$178.17	$178.15	$178.20
Purchase #6	$70.93	10.174%	$78.1464	$78.15	$78.15	$78.10
Purchase #7	$85.25	5.510%	$89.9473	$89.95	$89.95	$89.90
7 purchase totals =	$884.90		$984.4662	$984.47	$984.45	$984.40