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	$120.69	11.628%	$134.7238	$134.72	$134.70	$134.70
Purchase #2	$145.47	5.392%	$153.3137	$153.31	$153.30	$153.30
Purchase #3	$80.68	11.342%	$89.8307	$89.83	$89.85	$89.80
Purchase #4	$137.25	8.224%	$148.5374	$148.54	$148.55	$148.50
Purchase #5	$6.27	11.646%	$7.0002	$7.00	$7.00	$7.00
Purchase #6	$85.69	6.418%	$91.1896	$91.19	$91.20	$91.20
Purchase #7	$148.60	6.739%	$158.6142	$158.61	$158.60	$158.60
7 purchase totals =	$724.65		$783.2096	$783.20	$783.20	$783.10