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	$37.33	5.598%	$39.4197	$39.42	$39.40	$39.40
Purchase #2	$57.49	3.597%	$59.5579	$59.56	$59.55	$59.60
Purchase #3	$133.42	11.230%	$148.4031	$148.40	$148.40	$148.40
Purchase #4	$61.91	8.132%	$66.9445	$66.94	$66.95	$66.90
Purchase #5	$23.60	13.832%	$26.8644	$26.86	$26.85	$26.90
Purchase #6	$166.73	3.572%	$172.6856	$172.69	$172.70	$172.70
Purchase #7	$106.65	5.371%	$112.3782	$112.38	$112.40	$112.40
7 purchase totals =	$587.13		$626.2534	$626.25	$626.25	$626.30