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	$134.57	8.747%	$146.3408	$146.34	$146.35	$146.30
Purchase #2	$244.63	13.390%	$277.386	$277.39	$277.40	$277.40
Purchase #3	$84.54	9.547%	$92.611	$92.61	$92.60	$92.60
Purchase #4	$111.47	5.647%	$117.7647	$117.76	$117.75	$117.80
Purchase #5	$69.54	3.868%	$72.2298	$72.23	$72.25	$72.20
Purchase #6	$87.58	3.597%	$90.7303	$90.73	$90.75	$90.70
Purchase #7	$99.52	12.535%	$111.9948	$111.99	$112.00	$112.00
7 purchase totals =	$831.85		$909.0574	$909.05	$909.10	$909.00