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	$90.86	9.320%	$99.3282	$99.33	$99.35	$99.30
Purchase #2	$176.58	5.339%	$186.0076	$186.01	$186.00	$186.00
Purchase #3	$175.49	8.361%	$190.1627	$190.16	$190.15	$190.20
Purchase #4	$72.25	13.605%	$82.0796	$82.08	$82.10	$82.10
Purchase #5	$99.89	4.236%	$104.1213	$104.12	$104.10	$104.10
Purchase #6	$134.41	12.538%	$151.2623	$151.26	$151.25	$151.30
Purchase #7	$129.45	11.785%	$144.7057	$144.71	$144.70	$144.70
7 purchase totals =	$878.93		$957.6674	$957.67	$957.65	$957.70