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	$57.76	3.690%	$59.8913	$59.89	$59.90	$59.90
Purchase #2	$70.47	13.572%	$80.0342	$80.03	$80.05	$80.00
Purchase #3	$157.81	5.375%	$166.2923	$166.29	$166.30	$166.30
Purchase #4	$153.84	3.256%	$158.849	$158.85	$158.85	$158.80
Purchase #5	$171.89	7.260%	$184.3692	$184.37	$184.35	$184.40
Purchase #6	$46.63	10.585%	$51.5658	$51.57	$51.55	$51.60
Purchase #7	$16.67	13.601%	$18.9373	$18.94	$18.95	$18.90
7 purchase totals =	$675.07		$719.9391	$719.94	$719.95	$719.90