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	$112.49	11.818%	$125.7841	$125.78	$125.80	$125.80
Purchase #2	$15.94	9.500%	$17.4543	$17.45	$17.45	$17.50
Purchase #3	$36.99	7.647%	$39.8186	$39.82	$39.80	$39.80
Purchase #4	$132.92	13.846%	$151.3241	$151.32	$151.30	$151.30
Purchase #5	$131.94	10.494%	$145.7858	$145.79	$145.80	$145.80
Purchase #6	$158.28	5.760%	$167.3969	$167.40	$167.40	$167.40
Purchase #7	$94.83	5.844%	$100.3719	$100.37	$100.35	$100.40
7 purchase totals =	$683.39		$747.9357	$747.93	$747.90	$748.00