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	$130.89	12.686%	$147.4947	$147.49	$147.50	$147.50
Purchase #2	$29.82	4.233%	$31.0823	$31.08	$31.10	$31.10
Purchase #3	$226.60	10.348%	$250.0486	$250.05	$250.05	$250.00
Purchase #4	$9.98	4.719%	$10.451	$10.45	$10.45	$10.50
Purchase #5	$245.75	3.768%	$255.0099	$255.01	$255.00	$255.00
Purchase #6	$96.88	4.817%	$101.5467	$101.55	$101.55	$101.50
Purchase #7	$230.54	7.765%	$248.4414	$248.44	$248.45	$248.40
7 purchase totals =	$970.46		$1,044.0746	$1,044.07	$1,044.10	$1,044.00