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	$228.50	9.645%	$250.5388	$250.54	$250.55	$250.50
Purchase #2	$145.37	9.262%	$158.8342	$158.83	$158.85	$158.80
Purchase #3	$131.52	5.142%	$138.2828	$138.28	$138.30	$138.30
Purchase #4	$87.33	3.756%	$90.6101	$90.61	$90.60	$90.60
Purchase #5	$167.52	7.344%	$179.8227	$179.82	$179.80	$179.80
Purchase #6	$78.74	5.469%	$83.0463	$83.05	$83.05	$83.00
Purchase #7	$79.74	13.244%	$90.3008	$90.30	$90.30	$90.30
7 purchase totals =	$918.72		$991.4357	$991.43	$991.45	$991.30