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	$241.65	9.387%	$264.3337	$264.33	$264.35	$264.30
Purchase #2	$152.44	7.663%	$164.1215	$164.12	$164.10	$164.10
Purchase #3	$111.53	13.534%	$126.6245	$126.62	$126.60	$126.60
Purchase #4	$84.81	5.611%	$89.5687	$89.57	$89.55	$89.60
Purchase #5	$133.71	8.225%	$144.7076	$144.71	$144.70	$144.70
Purchase #6	$29.25	9.603%	$32.0589	$32.06	$32.05	$32.10
Purchase #7	$46.62	5.366%	$49.1216	$49.12	$49.10	$49.10
7 purchase totals =	$800.01		$870.5365	$870.53	$870.45	$870.50