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	$100.69	6.785%	$107.5218	$107.52	$107.50	$107.50
Purchase #2	$223.35	10.681%	$247.206	$247.21	$247.20	$247.20
Purchase #3	$130.34	6.865%	$139.2878	$139.29	$139.30	$139.30
Purchase #4	$9.43	9.152%	$10.293	$10.29	$10.30	$10.30
Purchase #5	$201.56	13.103%	$227.9704	$227.97	$227.95	$228.00
Purchase #6	$152.99	4.508%	$159.8868	$159.89	$159.90	$159.90
Purchase #7	$183.91	13.330%	$208.4252	$208.43	$208.45	$208.40
7 purchase totals =	$1,002.27		$1,100.5910	$1,100.60	$1,100.60	$1,100.60