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	$59.76	11.596%	$66.6898	$66.69	$66.70	$66.70
Purchase #2	$53.62	10.106%	$59.0388	$59.04	$59.05	$59.00
Purchase #3	$241.82	5.320%	$254.6848	$254.68	$254.70	$254.70
Purchase #4	$233.73	10.732%	$258.8139	$258.81	$258.80	$258.80
Purchase #5	$95.55	13.246%	$108.2066	$108.21	$108.20	$108.20
Purchase #6	$243.62	11.175%	$270.8445	$270.84	$270.85	$270.80
Purchase #7	$127.41	7.797%	$137.3442	$137.34	$137.35	$137.30
7 purchase totals =	$1,055.51		$1,155.6226	$1,155.61	$1,155.65	$1,155.50