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	$38.89	13.436%	$44.1153	$44.12	$44.10	$44.10
Purchase #2	$176.38	9.372%	$192.9103	$192.91	$192.90	$192.90
Purchase #3	$63.78	4.509%	$66.6558	$66.66	$66.65	$66.70
Purchase #4	$246.32	13.499%	$279.5707	$279.57	$279.55	$279.60
Purchase #5	$205.54	11.803%	$229.7999	$229.80	$229.80	$229.80
Purchase #6	$159.88	7.760%	$172.2867	$172.29	$172.30	$172.30
Purchase #7	$118.41	7.593%	$127.4009	$127.40	$127.40	$127.40
7 purchase totals =	$1,009.20		$1,112.7396	$1,112.75	$1,112.70	$1,112.80