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	$29.75	12.848%	$33.5723	$33.57	$33.55	$33.60
Purchase #2	$158.70	8.486%	$172.1673	$172.17	$172.15	$172.20
Purchase #3	$150.95	4.543%	$157.8077	$157.81	$157.80	$157.80
Purchase #4	$215.63	5.271%	$226.9959	$227.00	$227.00	$227.00
Purchase #5	$29.64	12.729%	$33.4129	$33.41	$33.40	$33.40
Purchase #6	$53.94	3.577%	$55.8694	$55.87	$55.85	$55.90
Purchase #7	$121.90	4.491%	$127.3745	$127.37	$127.35	$127.40
7 purchase totals =	$760.51		$807.2000	$807.20	$807.10	$807.30