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	$101.78	3.577%	$105.4207	$105.42	$105.40	$105.40
Purchase #2	$115.29	10.617%	$127.5303	$127.53	$127.55	$127.50
Purchase #3	$123.83	4.725%	$129.681	$129.68	$129.70	$129.70
Purchase #4	$207.33	11.215%	$230.5821	$230.58	$230.60	$230.60
Purchase #5	$230.78	5.690%	$243.9114	$243.91	$243.90	$243.90
Purchase #6	$168.70	13.527%	$191.52	$191.52	$191.50	$191.50
Purchase #7	$241.78	13.500%	$274.4203	$274.42	$274.40	$274.40
7 purchase totals =	$1,189.49		$1,303.0658	$1,303.06	$1,303.05	$1,303.00