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	$24.45	5.552%	$25.8075	$25.81	$25.80	$25.80
Purchase #2	$170.67	10.697%	$188.9266	$188.93	$188.95	$188.90
Purchase #3	$36.95	6.341%	$39.293	$39.29	$39.30	$39.30
Purchase #4	$219.79	13.467%	$249.3891	$249.39	$249.40	$249.40
Purchase #5	$38.71	9.830%	$42.5152	$42.52	$42.50	$42.50
Purchase #6	$44.84	10.328%	$49.4711	$49.47	$49.45	$49.50
Purchase #7	$30.83	5.264%	$32.4529	$32.45	$32.45	$32.50
7 purchase totals =	$566.24		$627.8554	$627.86	$627.85	$627.90