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	$156.84	7.355%	$168.3756	$168.38	$168.40	$168.40
Purchase #2	$51.65	11.736%	$57.7116	$57.71	$57.70	$57.70
Purchase #3	$51.90	7.273%	$55.6747	$55.67	$55.65	$55.70
Purchase #4	$32.77	13.370%	$37.1513	$37.15	$37.15	$37.20
Purchase #5	$130.67	11.379%	$145.5389	$145.54	$145.55	$145.50
Purchase #6	$45.51	6.286%	$48.3708	$48.37	$48.35	$48.40
Purchase #7	$15.28	3.628%	$15.8344	$15.83	$15.85	$15.80
7 purchase totals =	$484.62		$528.6573	$528.65	$528.65	$528.70