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	$26.75	5.493%	$28.2194	$28.22	$28.20	$28.20
Purchase #2	$30.45	9.372%	$33.3038	$33.30	$33.30	$33.30
Purchase #3	$186.50	12.516%	$209.8423	$209.84	$209.85	$209.80
Purchase #4	$81.51	11.301%	$90.7214	$90.72	$90.70	$90.70
Purchase #5	$18.63	10.252%	$20.5399	$20.54	$20.55	$20.50
Purchase #6	$77.69	7.202%	$83.2852	$83.29	$83.30	$83.30
Purchase #7	$96.39	11.636%	$107.6059	$107.61	$107.60	$107.60
7 purchase totals =	$517.92		$573.5179	$573.52	$573.50	$573.40