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	$40.77	13.580%	$46.3066	$46.31	$46.30	$46.30
Purchase #2	$102.82	4.436%	$107.3811	$107.38	$107.40	$107.40
Purchase #3	$94.91	11.334%	$105.6671	$105.67	$105.65	$105.70
Purchase #4	$96.87	5.128%	$101.8375	$101.84	$101.85	$101.80
Purchase #5	$27.48	5.476%	$28.9848	$28.98	$29.00	$29.00
Purchase #6	$111.78	13.803%	$127.209	$127.21	$127.20	$127.20
Purchase #7	$190.30	10.275%	$209.8533	$209.85	$209.85	$209.90
7 purchase totals =	$664.93		$727.2394	$727.24	$727.25	$727.30