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	$163.52	9.536%	$179.1133	$179.11	$179.10	$179.10
Purchase #2	$215.43	3.226%	$222.3798	$222.38	$222.40	$222.40
Purchase #3	$158.89	5.360%	$167.4065	$167.41	$167.40	$167.40
Purchase #4	$156.37	10.464%	$172.7326	$172.73	$172.75	$172.70
Purchase #5	$196.55	6.230%	$208.7951	$208.80	$208.80	$208.80
Purchase #6	$19.67	6.517%	$20.9519	$20.95	$20.95	$21.00
Purchase #7	$17.50	5.863%	$18.526	$18.53	$18.55	$18.50
7 purchase totals =	$927.93		$989.9052	$989.91	$989.95	$989.90