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	$206.35	12.103%	$231.3245	$231.32	$231.30	$231.30
Purchase #2	$113.84	10.853%	$126.1951	$126.20	$126.20	$126.20
Purchase #3	$209.56	5.154%	$220.3607	$220.36	$220.35	$220.40
Purchase #4	$138.26	9.333%	$151.1638	$151.16	$151.15	$151.20
Purchase #5	$185.71	5.697%	$196.2899	$196.29	$196.30	$196.30
Purchase #6	$10.87	12.672%	$12.2474	$12.25	$12.25	$12.20
Purchase #7	$49.82	10.273%	$54.938	$54.94	$54.95	$54.90
7 purchase totals =	$914.41		$992.5194	$992.52	$992.50	$992.50