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	$158.98	13.350%	$180.2038	$180.20	$180.20	$180.20
Purchase #2	$127.92	7.764%	$137.8517	$137.85	$137.85	$137.90
Purchase #3	$176.28	5.186%	$185.4219	$185.42	$185.40	$185.40
Purchase #4	$183.83	4.759%	$192.5785	$192.58	$192.60	$192.60
Purchase #5	$102.58	13.275%	$116.1975	$116.20	$116.20	$116.20
Purchase #6	$33.42	6.123%	$35.4663	$35.47	$35.45	$35.50
Purchase #7	$142.55	5.640%	$150.5898	$150.59	$150.60	$150.60
7 purchase totals =	$925.56		$998.3095	$998.31	$998.30	$998.40