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	$127.28	12.348%	$142.9965	$143.00	$143.00	$143.00
Purchase #2	$102.71	10.441%	$113.434	$113.43	$113.45	$113.40
Purchase #3	$150.66	9.805%	$165.4322	$165.43	$165.45	$165.40
Purchase #4	$106.25	11.483%	$118.4507	$118.45	$118.45	$118.50
Purchase #5	$131.59	13.857%	$149.8244	$149.82	$149.80	$149.80
Purchase #6	$41.62	5.792%	$44.0306	$44.03	$44.05	$44.00
Purchase #7	$148.84	11.137%	$165.4163	$165.42	$165.40	$165.40
7 purchase totals =	$808.95		$899.5847	$899.58	$899.60	$899.50