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	$22.32	4.426%	$23.3079	$23.31	$23.30	$23.30
Purchase #2	$127.31	9.292%	$139.1396	$139.14	$139.15	$139.10
Purchase #3	$224.51	5.643%	$237.1791	$237.18	$237.20	$237.20
Purchase #4	$62.60	5.451%	$66.0123	$66.01	$66.00	$66.00
Purchase #5	$47.57	13.688%	$54.0814	$54.08	$54.10	$54.10
Purchase #6	$76.61	4.396%	$79.9778	$79.98	$80.00	$80.00
Purchase #7	$62.62	7.786%	$67.4956	$67.50	$67.50	$67.50
7 purchase totals =	$623.54		$667.1937	$667.20	$667.25	$667.20