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	$11.66	8.334%	$12.6317	$12.63	$12.65	$12.60
Purchase #2	$234.60	11.795%	$262.2711	$262.27	$262.25	$262.30
Purchase #3	$8.91	12.388%	$10.0138	$10.01	$10.00	$10.00
Purchase #4	$207.29	13.294%	$234.8471	$234.85	$234.85	$234.80
Purchase #5	$119.95	9.624%	$131.494	$131.49	$131.50	$131.50
Purchase #6	$235.26	13.624%	$267.3118	$267.31	$267.30	$267.30
Purchase #7	$76.85	10.728%	$85.0945	$85.09	$85.10	$85.10
7 purchase totals =	$894.52		$1,003.6640	$1,003.65	$1,003.65	$1,003.60