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	$225.75	11.566%	$251.8602	$251.86	$251.85	$251.90
Purchase #2	$109.90	4.534%	$114.8829	$114.88	$114.90	$114.90
Purchase #3	$95.77	5.350%	$100.8937	$100.89	$100.90	$100.90
Purchase #4	$15.29	10.397%	$16.8797	$16.88	$16.90	$16.90
Purchase #5	$70.54	12.497%	$79.3554	$79.36	$79.35	$79.40
Purchase #6	$10.46	8.254%	$11.3234	$11.32	$11.30	$11.30
Purchase #7	$101.88	3.485%	$105.4305	$105.43	$105.45	$105.40
7 purchase totals =	$629.59		$680.6258	$680.62	$680.65	$680.70