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	$18.94	5.401%	$19.9629	$19.96	$19.95	$20.00
Purchase #2	$156.43	10.185%	$172.3624	$172.36	$172.35	$172.40
Purchase #3	$178.69	12.300%	$200.6689	$200.67	$200.65	$200.70
Purchase #4	$15.37	10.693%	$17.0135	$17.01	$17.00	$17.00
Purchase #5	$59.59	11.536%	$66.4643	$66.46	$66.45	$66.50
Purchase #6	$168.72	9.330%	$184.4616	$184.46	$184.45	$184.50
Purchase #7	$99.91	4.832%	$104.7377	$104.74	$104.75	$104.70
7 purchase totals =	$697.65		$765.6713	$765.66	$765.60	$765.80