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	$11.44	10.336%	$12.6224	$12.62	$12.60	$12.60
Purchase #2	$155.38	3.741%	$161.1928	$161.19	$161.20	$161.20
Purchase #3	$106.95	4.670%	$111.9446	$111.94	$111.95	$111.90
Purchase #4	$123.55	3.583%	$127.9768	$127.98	$128.00	$128.00
Purchase #5	$219.33	7.803%	$236.4443	$236.44	$236.45	$236.40
Purchase #6	$149.50	9.803%	$164.1555	$164.16	$164.15	$164.20
Purchase #7	$38.45	8.797%	$41.8324	$41.83	$41.85	$41.80
7 purchase totals =	$804.60		$856.1688	$856.16	$856.20	$856.10