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	$42.71	6.404%	$45.4451	$45.45	$45.45	$45.40
Purchase #2	$16.72	10.635%	$18.4982	$18.50	$18.50	$18.50
Purchase #3	$150.32	6.466%	$160.0397	$160.04	$160.05	$160.00
Purchase #4	$44.32	4.461%	$46.2971	$46.30	$46.30	$46.30
Purchase #5	$126.32	6.480%	$134.5055	$134.51	$134.50	$134.50
Purchase #6	$145.59	4.837%	$152.6322	$152.63	$152.65	$152.60
Purchase #7	$138.65	10.643%	$153.4065	$153.41	$153.40	$153.40
7 purchase totals =	$664.63		$710.8243	$710.84	$710.85	$710.70