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	$192.50	7.269%	$206.4928	$206.49	$206.50	$206.50
Purchase #2	$100.55	11.295%	$111.9071	$111.91	$111.90	$111.90
Purchase #3	$123.28	11.311%	$137.2242	$137.22	$137.20	$137.20
Purchase #4	$156.46	4.384%	$163.3192	$163.32	$163.30	$163.30
Purchase #5	$164.37	13.864%	$187.1583	$187.16	$187.15	$187.20
Purchase #6	$60.57	12.443%	$68.1067	$68.11	$68.10	$68.10
Purchase #7	$40.88	11.760%	$45.6875	$45.69	$45.70	$45.70
7 purchase totals =	$838.61		$919.8958	$919.90	$919.85	$919.90