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	$13.79	11.655%	$15.3972	$15.40	$15.40	$15.40
Purchase #2	$109.52	13.130%	$123.9	$123.90	$123.90	$123.90
Purchase #3	$153.84	7.525%	$165.4165	$165.42	$165.40	$165.40
Purchase #4	$188.48	10.579%	$208.4193	$208.42	$208.40	$208.40
Purchase #5	$100.61	7.613%	$108.2694	$108.27	$108.25	$108.30
Purchase #6	$12.67	8.807%	$13.7858	$13.79	$13.80	$13.80
Purchase #7	$125.32	4.286%	$130.6912	$130.69	$130.70	$130.70
7 purchase totals =	$704.23		$765.8794	$765.89	$765.85	$765.90