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	$62.85	12.594%	$70.7653	$70.77	$70.75	$70.80
Purchase #2	$126.89	10.143%	$139.7605	$139.76	$139.75	$139.80
Purchase #3	$188.54	9.647%	$206.7285	$206.73	$206.75	$206.70
Purchase #4	$52.91	12.466%	$59.5058	$59.51	$59.50	$59.50
Purchase #5	$145.34	4.840%	$152.3745	$152.37	$152.35	$152.40
Purchase #6	$167.81	5.848%	$177.6235	$177.62	$177.60	$177.60
Purchase #7	$19.52	10.543%	$21.578	$21.58	$21.60	$21.60
7 purchase totals =	$763.86		$828.3361	$828.34	$828.30	$828.40