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	$74.38	9.102%	$81.1501	$81.15	$81.15	$81.20
Purchase #2	$137.49	13.808%	$156.4746	$156.47	$156.45	$156.50
Purchase #3	$152.94	8.867%	$166.5012	$166.50	$166.50	$166.50
Purchase #4	$241.88	5.864%	$256.0638	$256.06	$256.05	$256.10
Purchase #5	$152.85	6.306%	$162.4887	$162.49	$162.50	$162.50
Purchase #6	$149.78	6.602%	$159.6685	$159.67	$159.65	$159.70
Purchase #7	$175.59	13.205%	$198.7767	$198.78	$198.80	$198.80
7 purchase totals =	$1,084.91		$1,181.1236	$1,181.12	$1,181.10	$1,181.30