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	$235.78	13.357%	$267.2731	$267.27	$267.25	$267.30
Purchase #2	$148.33	5.148%	$155.966	$155.97	$155.95	$156.00
Purchase #3	$95.85	7.465%	$103.0052	$103.01	$103.00	$103.00
Purchase #4	$61.49	9.622%	$67.4066	$67.41	$67.40	$67.40
Purchase #5	$151.87	13.518%	$172.3998	$172.40	$172.40	$172.40
Purchase #6	$98.82	4.563%	$103.3292	$103.33	$103.35	$103.30
Purchase #7	$66.86	10.763%	$74.0561	$74.06	$74.05	$74.10
7 purchase totals =	$859.00		$943.4360	$943.45	$943.40	$943.50