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	$143.38	6.565%	$152.7929	$152.79	$152.80	$152.80
Purchase #2	$242.52	4.114%	$252.4973	$252.50	$252.50	$252.50
Purchase #3	$30.91	5.124%	$32.4938	$32.49	$32.50	$32.50
Purchase #4	$55.48	12.865%	$62.6175	$62.62	$62.60	$62.60
Purchase #5	$52.44	8.754%	$57.0306	$57.03	$57.05	$57.00
Purchase #6	$35.78	9.835%	$39.299	$39.30	$39.30	$39.30
Purchase #7	$167.41	13.599%	$190.1761	$190.18	$190.20	$190.20
7 purchase totals =	$727.92		$786.9072	$786.91	$786.95	$786.90