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	$105.61	5.337%	$111.2464	$111.25	$111.25	$111.20
Purchase #2	$152.51	9.247%	$166.6126	$166.61	$166.60	$166.60
Purchase #3	$184.34	8.140%	$199.3453	$199.35	$199.35	$199.30
Purchase #4	$21.78	11.758%	$24.3409	$24.34	$24.35	$24.30
Purchase #5	$130.70	13.582%	$148.4517	$148.45	$148.45	$148.50
Purchase #6	$238.28	5.276%	$250.8517	$250.85	$250.85	$250.90
Purchase #7	$53.77	8.366%	$58.2684	$58.27	$58.25	$58.30
7 purchase totals =	$886.99		$959.1170	$959.12	$959.10	$959.10