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	$159.51	12.581%	$179.578	$179.58	$179.60	$179.60
Purchase #2	$141.50	12.113%	$158.6399	$158.64	$158.65	$158.60
Purchase #3	$144.75	4.235%	$150.8802	$150.88	$150.90	$150.90
Purchase #4	$93.29	6.442%	$99.2997	$99.30	$99.30	$99.30
Purchase #5	$89.35	3.546%	$92.5184	$92.52	$92.50	$92.50
Purchase #6	$87.52	3.313%	$90.4195	$90.42	$90.40	$90.40
Purchase #7	$164.45	6.595%	$175.2955	$175.30	$175.30	$175.30
7 purchase totals =	$880.37		$946.6312	$946.64	$946.65	$946.60