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	$51.95	9.820%	$57.0515	$57.05	$57.05	$57.10
Purchase #2	$115.70	9.838%	$127.0826	$127.08	$127.10	$127.10
Purchase #3	$89.34	12.629%	$100.6227	$100.62	$100.60	$100.60
Purchase #4	$209.93	10.106%	$231.1455	$231.15	$231.15	$231.10
Purchase #5	$131.42	6.143%	$139.4931	$139.49	$139.50	$139.50
Purchase #6	$180.35	7.155%	$193.254	$193.25	$193.25	$193.30
Purchase #7	$150.29	5.517%	$158.5815	$158.58	$158.60	$158.60
7 purchase totals =	$928.98		$1,007.2309	$1,007.22	$1,007.25	$1,007.30