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	$173.72	6.615%	$185.2116	$185.21	$185.20	$185.20
Purchase #2	$153.50	8.315%	$166.2635	$166.26	$166.25	$166.30
Purchase #3	$222.67	11.615%	$248.5331	$248.53	$248.55	$248.50
Purchase #4	$46.38	12.148%	$52.0142	$52.01	$52.00	$52.00
Purchase #5	$231.43	11.670%	$258.4379	$258.44	$258.45	$258.40
Purchase #6	$230.94	10.521%	$255.2372	$255.24	$255.25	$255.20
Purchase #7	$33.60	3.754%	$34.8613	$34.86	$34.85	$34.90
7 purchase totals =	$1,092.24		$1,200.5588	$1,200.55	$1,200.55	$1,200.50