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	$17.76	13.478%	$20.1537	$20.15	$20.15	$20.20
Purchase #2	$11.53	4.657%	$12.067	$12.07	$12.05	$12.10
Purchase #3	$59.95	13.217%	$67.8736	$67.87	$67.85	$67.90
Purchase #4	$174.89	6.331%	$185.9623	$185.96	$185.95	$186.00
Purchase #5	$230.85	4.750%	$241.8154	$241.82	$241.80	$241.80
Purchase #6	$35.85	5.628%	$37.8676	$37.87	$37.85	$37.90
Purchase #7	$156.56	3.220%	$161.6012	$161.60	$161.60	$161.60
7 purchase totals =	$687.39		$727.3408	$727.34	$727.25	$727.50