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	$78.56	6.202%	$83.4323	$83.43	$83.45	$83.40
Purchase #2	$36.77	4.848%	$38.5526	$38.55	$38.55	$38.60
Purchase #3	$163.31	13.599%	$185.5185	$185.52	$185.50	$185.50
Purchase #4	$30.90	5.193%	$32.5046	$32.50	$32.50	$32.50
Purchase #5	$56.95	11.165%	$63.3085	$63.31	$63.30	$63.30
Purchase #6	$202.93	13.464%	$230.2525	$230.25	$230.25	$230.30
Purchase #7	$211.51	12.610%	$238.1814	$238.18	$238.20	$238.20
7 purchase totals =	$780.93		$871.7504	$871.74	$871.75	$871.80