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	$23.70	5.718%	$25.0552	$25.06	$25.05	$25.10
Purchase #2	$171.81	7.197%	$184.1752	$184.18	$184.20	$184.20
Purchase #3	$19.78	3.122%	$20.3975	$20.40	$20.40	$20.40
Purchase #4	$81.42	11.672%	$90.9233	$90.92	$90.90	$90.90
Purchase #5	$54.51	12.788%	$61.4807	$61.48	$61.50	$61.50
Purchase #6	$137.64	10.130%	$151.5829	$151.58	$151.60	$151.60
Purchase #7	$47.53	3.162%	$49.0329	$49.03	$49.05	$49.00
7 purchase totals =	$536.39		$582.6477	$582.65	$582.70	$582.70