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	$89.58	6.485%	$95.3893	$95.39	$95.40	$95.40
Purchase #2	$47.42	13.295%	$53.7245	$53.72	$53.70	$53.70
Purchase #3	$18.89	10.692%	$20.9097	$20.91	$20.90	$20.90
Purchase #4	$104.62	11.394%	$116.5404	$116.54	$116.55	$116.50
Purchase #5	$108.82	8.793%	$118.3885	$118.39	$118.40	$118.40
Purchase #6	$118.91	6.704%	$126.8817	$126.88	$126.90	$126.90
Purchase #7	$66.92	11.807%	$74.8212	$74.82	$74.80	$74.80
7 purchase totals =	$555.16		$606.6553	$606.65	$606.65	$606.60