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	$131.46	5.348%	$138.4905	$138.49	$138.50	$138.50
Purchase #2	$147.41	8.579%	$160.0563	$160.06	$160.05	$160.10
Purchase #3	$53.89	5.597%	$56.9062	$56.91	$56.90	$56.90
Purchase #4	$193.28	6.731%	$206.2897	$206.29	$206.30	$206.30
Purchase #5	$242.84	5.343%	$255.8149	$255.81	$255.80	$255.80
Purchase #6	$38.32	4.621%	$40.0908	$40.09	$40.10	$40.10
Purchase #7	$200.85	3.848%	$208.5787	$208.58	$208.60	$208.60
7 purchase totals =	$1,008.05		$1,066.2271	$1,066.23	$1,066.25	$1,066.30