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	$154.29	10.212%	$170.0461	$170.05	$170.05	$170.00
Purchase #2	$63.28	10.707%	$70.0554	$70.06	$70.05	$70.10
Purchase #3	$100.47	4.586%	$105.0776	$105.08	$105.10	$105.10
Purchase #4	$156.98	7.331%	$168.4882	$168.49	$168.50	$168.50
Purchase #5	$70.61	8.470%	$76.5907	$76.59	$76.60	$76.60
Purchase #6	$153.68	3.756%	$159.4522	$159.45	$159.45	$159.50
Purchase #7	$73.39	6.849%	$78.4165	$78.42	$78.40	$78.40
7 purchase totals =	$772.70		$828.1267	$828.14	$828.15	$828.20