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	$37.59	10.619%	$41.5817	$41.58	$41.60	$41.60
Purchase #2	$132.28	8.731%	$143.8294	$143.83	$143.85	$143.80
Purchase #3	$72.72	11.426%	$81.029	$81.03	$81.05	$81.00
Purchase #4	$110.37	7.454%	$118.597	$118.60	$118.60	$118.60
Purchase #5	$30.37	4.407%	$31.7084	$31.71	$31.70	$31.70
Purchase #6	$152.59	7.719%	$164.3684	$164.37	$164.35	$164.40
Purchase #7	$229.72	13.274%	$260.213	$260.21	$260.20	$260.20
7 purchase totals =	$765.64		$841.3269	$841.33	$841.35	$841.30