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	$138.95	10.224%	$153.1562	$153.16	$153.15	$153.20
Purchase #2	$164.91	12.145%	$184.9383	$184.94	$184.95	$184.90
Purchase #3	$126.92	13.137%	$143.5935	$143.59	$143.60	$143.60
Purchase #4	$93.33	13.457%	$105.8894	$105.89	$105.90	$105.90
Purchase #5	$15.76	13.866%	$17.9453	$17.95	$17.95	$17.90
Purchase #6	$129.68	7.801%	$139.7963	$139.80	$139.80	$139.80
Purchase #7	$64.78	4.311%	$67.5727	$67.57	$67.55	$67.60
7 purchase totals =	$734.33		$812.8917	$812.90	$812.90	$812.90