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	$100.81	10.528%	$111.4233	$111.42	$111.40	$111.40
Purchase #2	$151.52	13.401%	$171.8252	$171.83	$171.85	$171.80
Purchase #3	$132.29	10.868%	$146.6673	$146.67	$146.65	$146.70
Purchase #4	$152.92	7.407%	$164.2468	$164.25	$164.25	$164.20
Purchase #5	$47.86	3.221%	$49.4016	$49.40	$49.40	$49.40
Purchase #6	$30.67	9.859%	$33.6938	$33.69	$33.70	$33.70
Purchase #7	$188.72	5.472%	$199.0468	$199.05	$199.05	$199.00
7 purchase totals =	$804.79		$876.3048	$876.31	$876.30	$876.20