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	$9.52	12.603%	$10.7198	$10.72	$10.70	$10.70
Purchase #2	$105.72	5.842%	$111.8962	$111.90	$111.90	$111.90
Purchase #3	$218.60	12.636%	$246.2223	$246.22	$246.20	$246.20
Purchase #4	$103.66	13.403%	$117.5535	$117.55	$117.55	$117.60
Purchase #5	$97.47	8.145%	$105.4089	$105.41	$105.40	$105.40
Purchase #6	$167.89	4.443%	$175.3494	$175.35	$175.35	$175.30
Purchase #7	$42.78	4.777%	$44.8236	$44.82	$44.80	$44.80
7 purchase totals =	$745.64		$811.9737	$811.97	$811.90	$811.90