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	$132.40	8.234%	$143.3018	$143.30	$143.30	$143.30
Purchase #2	$59.57	6.140%	$63.2276	$63.23	$63.25	$63.20
Purchase #3	$41.91	6.535%	$44.6488	$44.65	$44.65	$44.60
Purchase #4	$13.97	6.281%	$14.8475	$14.85	$14.85	$14.80
Purchase #5	$40.28	5.392%	$42.4519	$42.45	$42.45	$42.50
Purchase #6	$59.28	12.452%	$66.6615	$66.66	$66.65	$66.70
Purchase #7	$235.88	12.122%	$264.4734	$264.47	$264.45	$264.50
7 purchase totals =	$583.29		$639.6125	$639.61	$639.60	$639.60