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	$245.48	13.748%	$279.2286	$279.23	$279.25	$279.20
Purchase #2	$68.49	5.641%	$72.3535	$72.35	$72.35	$72.40
Purchase #3	$17.55	4.573%	$18.3526	$18.35	$18.35	$18.40
Purchase #4	$167.60	10.736%	$185.5935	$185.59	$185.60	$185.60
Purchase #5	$60.25	13.327%	$68.2795	$68.28	$68.30	$68.30
Purchase #6	$154.87	8.752%	$168.4242	$168.42	$168.40	$168.40
Purchase #7	$37.29	6.390%	$39.6728	$39.67	$39.65	$39.70
7 purchase totals =	$751.53		$831.9047	$831.89	$831.90	$832.00