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	$62.53	13.292%	$70.8415	$70.84	$70.85	$70.80
Purchase #2	$38.75	4.106%	$40.3411	$40.34	$40.35	$40.30
Purchase #3	$232.68	13.653%	$264.4478	$264.45	$264.45	$264.40
Purchase #4	$158.70	8.472%	$172.1451	$172.15	$172.15	$172.10
Purchase #5	$233.48	9.541%	$255.7563	$255.76	$255.75	$255.80
Purchase #6	$164.82	5.434%	$173.7763	$173.78	$173.80	$173.80
Purchase #7	$52.89	12.404%	$59.4505	$59.45	$59.45	$59.50
7 purchase totals =	$943.85		$1,036.7586	$1,036.77	$1,036.80	$1,036.70