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	$16.97	13.854%	$19.321	$19.32	$19.30	$19.30
Purchase #2	$51.63	8.105%	$55.8146	$55.81	$55.80	$55.80
Purchase #3	$79.66	12.781%	$89.8413	$89.84	$89.85	$89.80
Purchase #4	$206.76	8.715%	$224.7791	$224.78	$224.80	$224.80
Purchase #5	$12.57	7.419%	$13.5026	$13.50	$13.50	$13.50
Purchase #6	$9.94	6.637%	$10.5997	$10.60	$10.60	$10.60
Purchase #7	$172.45	8.867%	$187.7411	$187.74	$187.75	$187.70
7 purchase totals =	$549.98		$601.5994	$601.59	$601.60	$601.50