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	$166.56	12.538%	$187.4433	$187.44	$187.45	$187.40
Purchase #2	$119.76	12.205%	$134.3767	$134.38	$134.40	$134.40
Purchase #3	$91.87	4.493%	$95.9977	$96.00	$96.00	$96.00
Purchase #4	$228.82	13.221%	$259.0723	$259.07	$259.05	$259.10
Purchase #5	$46.81	13.355%	$53.0615	$53.06	$53.05	$53.10
Purchase #6	$40.92	4.104%	$42.5994	$42.60	$42.60	$42.60
Purchase #7	$213.86	9.194%	$233.5223	$233.52	$233.50	$233.50
7 purchase totals =	$908.60		$1,006.0732	$1,006.07	$1,006.05	$1,006.10