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	$21.27	10.323%	$23.4657	$23.47	$23.45	$23.50
Purchase #2	$119.80	6.446%	$127.5223	$127.52	$127.50	$127.50
Purchase #3	$153.61	12.659%	$173.0555	$173.06	$173.05	$173.10
Purchase #4	$168.29	7.225%	$180.449	$180.45	$180.45	$180.40
Purchase #5	$204.99	7.282%	$219.9174	$219.92	$219.90	$219.90
Purchase #6	$100.32	5.204%	$105.5407	$105.54	$105.55	$105.50
Purchase #7	$151.92	7.253%	$162.9388	$162.94	$162.95	$162.90
7 purchase totals =	$920.20		$992.8894	$992.90	$992.85	$992.80