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	$240.73	12.338%	$270.4313	$270.43	$270.45	$270.40
Purchase #2	$242.44	5.294%	$255.2748	$255.27	$255.25	$255.30
Purchase #3	$81.65	10.577%	$90.2861	$90.29	$90.30	$90.30
Purchase #4	$49.30	9.386%	$53.9273	$53.93	$53.95	$53.90
Purchase #5	$216.29	5.237%	$227.6171	$227.62	$227.60	$227.60
Purchase #6	$32.27	4.109%	$33.596	$33.60	$33.60	$33.60
Purchase #7	$101.72	11.113%	$113.0241	$113.02	$113.00	$113.00
7 purchase totals =	$964.40		$1,044.1567	$1,044.16	$1,044.15	$1,044.10