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	$20.80	11.648%	$23.2228	$23.22	$23.20	$23.20
Purchase #2	$131.51	10.688%	$145.5658	$145.57	$145.55	$145.60
Purchase #3	$80.48	4.108%	$83.7861	$83.79	$83.80	$83.80
Purchase #4	$143.45	6.189%	$152.3281	$152.33	$152.35	$152.30
Purchase #5	$168.35	12.599%	$189.5604	$189.56	$189.55	$189.60
Purchase #6	$118.55	7.462%	$127.3962	$127.40	$127.40	$127.40
Purchase #7	$158.63	8.629%	$172.3182	$172.32	$172.30	$172.30
7 purchase totals =	$821.77		$894.1776	$894.19	$894.15	$894.20