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	$169.69	12.128%	$190.27	$190.27	$190.25	$190.30
Purchase #2	$47.38	4.405%	$49.4671	$49.47	$49.45	$49.50
Purchase #3	$131.78	9.714%	$144.5811	$144.58	$144.60	$144.60
Purchase #4	$114.51	7.546%	$123.1509	$123.15	$123.15	$123.20
Purchase #5	$20.63	12.105%	$23.1273	$23.13	$23.15	$23.10
Purchase #6	$83.27	9.796%	$91.4271	$91.43	$91.45	$91.40
Purchase #7	$104.56	12.607%	$117.7419	$117.74	$117.75	$117.70
7 purchase totals =	$671.82		$739.7654	$739.77	$739.80	$739.80