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	$16.42	4.169%	$17.1045	$17.10	$17.10	$17.10
Purchase #2	$159.45	7.481%	$171.3785	$171.38	$171.40	$171.40
Purchase #3	$67.87	6.580%	$72.3358	$72.34	$72.35	$72.30
Purchase #4	$127.70	9.213%	$139.465	$139.47	$139.45	$139.50
Purchase #5	$101.91	9.719%	$111.8146	$111.81	$111.80	$111.80
Purchase #6	$206.33	6.168%	$219.0564	$219.06	$219.05	$219.10
Purchase #7	$170.53	5.580%	$180.0456	$180.05	$180.05	$180.00
7 purchase totals =	$850.21		$911.2004	$911.21	$911.20	$911.20