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	$129.98	6.861%	$138.8979	$138.90	$138.90	$138.90
Purchase #2	$167.66	9.404%	$183.4267	$183.43	$183.45	$183.40
Purchase #3	$38.28	5.833%	$40.5129	$40.51	$40.50	$40.50
Purchase #4	$86.66	3.398%	$89.6047	$89.60	$89.60	$89.60
Purchase #5	$82.75	5.351%	$87.178	$87.18	$87.20	$87.20
Purchase #6	$33.58	8.299%	$36.3668	$36.37	$36.35	$36.40
Purchase #7	$34.63	11.500%	$38.6125	$38.61	$38.60	$38.60
7 purchase totals =	$573.54		$614.5995	$614.60	$614.60	$614.60