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	$114.89	12.382%	$129.1157	$129.12	$129.10	$129.10
Purchase #2	$66.90	8.240%	$72.4126	$72.41	$72.40	$72.40
Purchase #3	$217.70	7.177%	$233.3243	$233.32	$233.30	$233.30
Purchase #4	$45.93	13.804%	$52.2702	$52.27	$52.25	$52.30
Purchase #5	$18.77	11.866%	$20.9972	$21.00	$21.00	$21.00
Purchase #6	$138.75	8.532%	$150.5882	$150.59	$150.60	$150.60
Purchase #7	$198.42	5.481%	$209.2954	$209.30	$209.30	$209.30
7 purchase totals =	$801.36		$868.0036	$868.01	$867.95	$868.00