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	$24.72	10.388%	$27.2879	$27.29	$27.30	$27.30
Purchase #2	$231.50	6.682%	$246.9688	$246.97	$246.95	$247.00
Purchase #3	$18.89	12.818%	$21.3113	$21.31	$21.30	$21.30
Purchase #4	$36.94	5.103%	$38.825	$38.83	$38.85	$38.80
Purchase #5	$40.98	10.757%	$45.3882	$45.39	$45.40	$45.40
Purchase #6	$30.81	5.231%	$32.4217	$32.42	$32.40	$32.40
Purchase #7	$192.78	3.817%	$200.1384	$200.14	$200.15	$200.10
7 purchase totals =	$576.62		$612.3413	$612.35	$612.35	$612.30