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	$158.61	8.659%	$172.344	$172.34	$172.35	$172.30
Purchase #2	$235.66	6.154%	$250.1625	$250.16	$250.15	$250.20
Purchase #3	$244.50	7.440%	$262.6908	$262.69	$262.70	$262.70
Purchase #4	$51.43	4.111%	$53.5443	$53.54	$53.55	$53.50
Purchase #5	$100.90	10.874%	$111.8719	$111.87	$111.85	$111.90
Purchase #6	$57.32	11.405%	$63.8573	$63.86	$63.85	$63.90
Purchase #7	$69.86	10.130%	$76.9368	$76.94	$76.95	$76.90
7 purchase totals =	$918.28		$991.4076	$991.40	$991.40	$991.40