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	$24.37	11.423%	$27.1538	$27.15	$27.15	$27.20
Purchase #2	$100.91	4.843%	$105.7971	$105.80	$105.80	$105.80
Purchase #3	$107.65	10.685%	$119.1524	$119.15	$119.15	$119.20
Purchase #4	$83.70	8.296%	$90.6438	$90.64	$90.65	$90.60
Purchase #5	$77.91	6.343%	$82.8518	$82.85	$82.85	$82.90
Purchase #6	$173.66	10.589%	$192.0489	$192.05	$192.05	$192.00
Purchase #7	$244.63	12.454%	$275.0962	$275.10	$275.10	$275.10
7 purchase totals =	$812.83		$892.7440	$892.74	$892.75	$892.80