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	$74.32	5.716%	$78.5681	$78.57	$78.55	$78.60
Purchase #2	$160.40	7.774%	$172.8695	$172.87	$172.85	$172.90
Purchase #3	$109.41	13.670%	$124.3663	$124.37	$124.35	$124.40
Purchase #4	$16.91	5.364%	$17.8171	$17.82	$17.80	$17.80
Purchase #5	$74.67	4.253%	$77.8457	$77.85	$77.85	$77.80
Purchase #6	$113.77	4.114%	$118.4505	$118.45	$118.45	$118.50
Purchase #7	$145.99	3.353%	$150.885	$150.89	$150.90	$150.90
7 purchase totals =	$695.47		$740.8022	$740.82	$740.75	$740.90