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	$148.85	11.428%	$165.8606	$165.86	$165.85	$165.90
Purchase #2	$173.61	7.715%	$187.004	$187.00	$187.00	$187.00
Purchase #3	$163.52	9.873%	$179.6643	$179.66	$179.65	$179.70
Purchase #4	$50.58	12.143%	$56.7219	$56.72	$56.70	$56.70
Purchase #5	$173.46	3.331%	$179.238	$179.24	$179.25	$179.20
Purchase #6	$172.49	7.394%	$185.2439	$185.24	$185.25	$185.20
Purchase #7	$217.92	3.662%	$225.9002	$225.90	$225.90	$225.90
7 purchase totals =	$1,100.43		$1,179.6329	$1,179.62	$1,179.60	$1,179.60