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	$132.46	4.631%	$138.5942	$138.59	$138.60	$138.60
Purchase #2	$32.86	6.238%	$34.9098	$34.91	$34.90	$34.90
Purchase #3	$186.65	13.135%	$211.1665	$211.17	$211.15	$211.20
Purchase #4	$158.46	6.598%	$168.9152	$168.92	$168.90	$168.90
Purchase #5	$13.90	5.339%	$14.6421	$14.64	$14.65	$14.60
Purchase #6	$55.41	12.175%	$62.1562	$62.16	$62.15	$62.20
Purchase #7	$62.42	12.871%	$70.4541	$70.45	$70.45	$70.50
7 purchase totals =	$642.16		$700.8381	$700.84	$700.80	$700.90