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	$184.43	3.194%	$190.3207	$190.32	$190.30	$190.30
Purchase #2	$237.27	13.428%	$269.1306	$269.13	$269.15	$269.10
Purchase #3	$101.60	8.729%	$110.4687	$110.47	$110.45	$110.50
Purchase #4	$111.97	4.145%	$116.6112	$116.61	$116.60	$116.60
Purchase #5	$117.75	4.707%	$123.2925	$123.29	$123.30	$123.30
Purchase #6	$86.30	4.827%	$90.4657	$90.47	$90.45	$90.50
Purchase #7	$38.69	5.627%	$40.8671	$40.87	$40.85	$40.90
7 purchase totals =	$878.01		$941.1565	$941.16	$941.10	$941.20