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	$95.69	5.140%	$100.6085	$100.61	$100.60	$100.60
Purchase #2	$52.75	13.753%	$60.0047	$60.00	$60.00	$60.00
Purchase #3	$99.40	4.761%	$104.1324	$104.13	$104.15	$104.10
Purchase #4	$74.73	8.568%	$81.1329	$81.13	$81.15	$81.10
Purchase #5	$165.80	5.417%	$174.7814	$174.78	$174.80	$174.80
Purchase #6	$107.51	12.265%	$120.6961	$120.70	$120.70	$120.70
Purchase #7	$152.81	12.630%	$172.1099	$172.11	$172.10	$172.10
7 purchase totals =	$748.69		$813.4659	$813.46	$813.50	$813.40