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	$246.33	13.627%	$279.8974	$279.90	$279.90	$279.90
Purchase #2	$165.98	13.277%	$188.0172	$188.02	$188.00	$188.00
Purchase #3	$153.72	9.555%	$168.4079	$168.41	$168.40	$168.40
Purchase #4	$13.52	11.710%	$15.1032	$15.10	$15.10	$15.10
Purchase #5	$21.52	12.847%	$24.2847	$24.28	$24.30	$24.30
Purchase #6	$121.66	5.349%	$128.1676	$128.17	$128.15	$128.20
Purchase #7	$9.59	9.697%	$10.5199	$10.52	$10.50	$10.50
7 purchase totals =	$732.32		$814.3979	$814.40	$814.35	$814.40