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	$228.60	11.290%	$254.4089	$254.41	$254.40	$254.40
Purchase #2	$156.32	10.532%	$172.7836	$172.78	$172.80	$172.80
Purchase #3	$81.41	11.549%	$90.812	$90.81	$90.80	$90.80
Purchase #4	$242.87	5.395%	$255.9728	$255.97	$255.95	$256.00
Purchase #5	$64.54	7.703%	$69.5115	$69.51	$69.50	$69.50
Purchase #6	$213.27	12.240%	$239.3742	$239.37	$239.35	$239.40
Purchase #7	$118.75	7.747%	$127.9496	$127.95	$127.95	$127.90
7 purchase totals =	$1,105.76		$1,210.8126	$1,210.80	$1,210.75	$1,210.80