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	$157.83	9.362%	$172.606	$172.61	$172.60	$172.60
Purchase #2	$250.82	11.621%	$279.9678	$279.97	$279.95	$280.00
Purchase #3	$75.32	13.845%	$85.7481	$85.75	$85.75	$85.70
Purchase #4	$47.42	12.510%	$53.3522	$53.35	$53.35	$53.40
Purchase #5	$54.77	12.262%	$61.4859	$61.49	$61.50	$61.50
Purchase #6	$77.93	3.668%	$80.7885	$80.79	$80.80	$80.80
Purchase #7	$198.85	3.683%	$206.1736	$206.17	$206.15	$206.20
7 purchase totals =	$862.94		$940.1221	$940.13	$940.10	$940.20