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	$70.82	10.269%	$78.0925	$78.09	$78.10	$78.10
Purchase #2	$189.85	3.379%	$196.265	$196.27	$196.25	$196.30
Purchase #3	$107.56	12.601%	$121.1136	$121.11	$121.10	$121.10
Purchase #4	$67.37	4.772%	$70.5849	$70.58	$70.60	$70.60
Purchase #5	$122.85	9.473%	$134.4876	$134.49	$134.50	$134.50
Purchase #6	$33.56	12.449%	$37.7379	$37.74	$37.75	$37.70
Purchase #7	$155.88	8.772%	$169.5538	$169.55	$169.55	$169.60
7 purchase totals =	$747.89		$807.8353	$807.83	$807.85	$807.90