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	$94.81	5.373%	$99.9041	$99.90	$99.90	$99.90
Purchase #2	$214.81	7.269%	$230.4245	$230.42	$230.40	$230.40
Purchase #3	$208.88	4.863%	$219.0378	$219.04	$219.05	$219.00
Purchase #4	$41.77	13.541%	$47.4261	$47.43	$47.45	$47.40
Purchase #5	$233.76	10.702%	$258.777	$258.78	$258.80	$258.80
Purchase #6	$77.82	7.144%	$83.3795	$83.38	$83.40	$83.40
Purchase #7	$169.29	7.455%	$181.9106	$181.91	$181.90	$181.90
7 purchase totals =	$1,041.14		$1,120.8596	$1,120.86	$1,120.90	$1,120.80