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	$26.51	9.544%	$29.0401	$29.04	$29.05	$29.00
Purchase #2	$115.69	10.107%	$127.3828	$127.38	$127.40	$127.40
Purchase #3	$38.43	11.402%	$42.8118	$42.81	$42.80	$42.80
Purchase #4	$127.97	7.466%	$137.5242	$137.52	$137.50	$137.50
Purchase #5	$137.63	6.667%	$146.8058	$146.81	$146.80	$146.80
Purchase #6	$214.61	7.384%	$230.4568	$230.46	$230.45	$230.50
Purchase #7	$187.29	8.828%	$203.824	$203.82	$203.80	$203.80
7 purchase totals =	$848.13		$917.8455	$917.84	$917.80	$917.80