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	$36.28	3.485%	$37.5444	$37.54	$37.55	$37.50
Purchase #2	$20.27	6.323%	$21.5517	$21.55	$21.55	$21.60
Purchase #3	$211.70	11.544%	$236.1386	$236.14	$236.15	$236.10
Purchase #4	$154.77	13.592%	$175.8063	$175.81	$175.80	$175.80
Purchase #5	$59.89	3.299%	$61.8658	$61.87	$61.85	$61.90
Purchase #6	$80.91	5.404%	$85.2824	$85.28	$85.30	$85.30
Purchase #7	$231.55	3.103%	$238.735	$238.74	$238.75	$238.70
7 purchase totals =	$795.37		$856.9242	$856.93	$856.95	$856.90