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	$179.53	3.333%	$185.5137	$185.51	$185.50	$185.50
Purchase #2	$108.30	10.848%	$120.0484	$120.05	$120.05	$120.00
Purchase #3	$245.34	11.175%	$272.7567	$272.76	$272.75	$272.80
Purchase #4	$44.30	3.297%	$45.7606	$45.76	$45.75	$45.80
Purchase #5	$192.31	10.861%	$213.1968	$213.20	$213.20	$213.20
Purchase #6	$112.61	13.307%	$127.595	$127.60	$127.60	$127.60
Purchase #7	$20.63	6.255%	$21.9204	$21.92	$21.90	$21.90
7 purchase totals =	$903.02		$986.7916	$986.80	$986.75	$986.80