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	$52.90	13.235%	$59.9013	$59.90	$59.90	$59.90
Purchase #2	$248.97	9.319%	$272.1715	$272.17	$272.15	$272.20
Purchase #3	$130.43	8.364%	$141.3392	$141.34	$141.35	$141.30
Purchase #4	$64.43	13.334%	$73.0211	$73.02	$73.00	$73.00
Purchase #5	$126.25	8.834%	$137.4029	$137.40	$137.40	$137.40
Purchase #6	$153.37	3.392%	$158.5723	$158.57	$158.55	$158.60
Purchase #7	$56.69	4.866%	$59.4485	$59.45	$59.45	$59.40
7 purchase totals =	$833.04		$901.8568	$901.85	$901.80	$901.80