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	$61.37	3.864%	$63.7413	$63.74	$63.75	$63.70
Purchase #2	$226.73	7.102%	$242.8324	$242.83	$242.85	$242.80
Purchase #3	$141.55	8.239%	$153.2123	$153.21	$153.20	$153.20
Purchase #4	$11.36	13.324%	$12.8736	$12.87	$12.85	$12.90
Purchase #5	$100.25	12.321%	$112.6018	$112.60	$112.60	$112.60
Purchase #6	$30.96	9.509%	$33.904	$33.90	$33.90	$33.90
Purchase #7	$47.61	5.803%	$50.3728	$50.37	$50.35	$50.40
7 purchase totals =	$619.83		$669.5382	$669.52	$669.50	$669.50