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	$111.39	13.256%	$126.1559	$126.16	$126.15	$126.20
Purchase #2	$87.62	4.831%	$91.8529	$91.85	$91.85	$91.90
Purchase #3	$37.73	5.725%	$39.89	$39.89	$39.90	$39.90
Purchase #4	$17.26	8.768%	$18.7734	$18.77	$18.75	$18.80
Purchase #5	$25.89	5.660%	$27.3554	$27.36	$27.35	$27.40
Purchase #6	$100.81	13.501%	$114.4204	$114.42	$114.40	$114.40
Purchase #7	$96.53	9.259%	$105.4677	$105.47	$105.45	$105.50
7 purchase totals =	$477.23		$523.9157	$523.92	$523.85	$524.10