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	$245.40	8.187%	$265.4909	$265.49	$265.50	$265.50
Purchase #2	$239.52	11.222%	$266.3989	$266.40	$266.40	$266.40
Purchase #3	$86.84	4.538%	$90.7808	$90.78	$90.80	$90.80
Purchase #4	$137.68	5.542%	$145.3102	$145.31	$145.30	$145.30
Purchase #5	$10.88	8.166%	$11.7685	$11.77	$11.75	$11.80
Purchase #6	$152.36	11.205%	$169.4319	$169.43	$169.45	$169.40
Purchase #7	$126.44	10.244%	$139.3925	$139.39	$139.40	$139.40
7 purchase totals =	$999.12		$1,088.5737	$1,088.57	$1,088.60	$1,088.60