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	$12.84	8.201%	$13.893	$13.89	$13.90	$13.90
Purchase #2	$57.76	12.608%	$65.0424	$65.04	$65.05	$65.00
Purchase #3	$153.57	10.162%	$169.1758	$169.18	$169.20	$169.20
Purchase #4	$96.94	4.663%	$101.4603	$101.46	$101.45	$101.50
Purchase #5	$188.84	4.250%	$196.8657	$196.87	$196.85	$196.90
Purchase #6	$32.27	12.464%	$36.2921	$36.29	$36.30	$36.30
Purchase #7	$8.78	10.383%	$9.6916	$9.69	$9.70	$9.70
7 purchase totals =	$551.00		$592.4209	$592.42	$592.45	$592.50