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	$143.43	13.286%	$162.4861	$162.49	$162.50	$162.50
Purchase #2	$19.92	11.112%	$22.1335	$22.13	$22.15	$22.10
Purchase #3	$20.78	4.292%	$21.6719	$21.67	$21.65	$21.70
Purchase #4	$233.54	13.263%	$264.5144	$264.51	$264.50	$264.50
Purchase #5	$16.77	8.680%	$18.2256	$18.23	$18.25	$18.20
Purchase #6	$249.99	11.825%	$279.5513	$279.55	$279.55	$279.60
Purchase #7	$55.27	12.691%	$62.2843	$62.28	$62.30	$62.30
7 purchase totals =	$739.70		$830.8671	$830.86	$830.90	$830.90