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	$79.47	12.716%	$89.5754	$89.58	$89.60	$89.60
Purchase #2	$164.55	13.400%	$186.5997	$186.60	$186.60	$186.60
Purchase #3	$139.28	9.183%	$152.0701	$152.07	$152.05	$152.10
Purchase #4	$34.31	9.461%	$37.5561	$37.56	$37.55	$37.60
Purchase #5	$51.86	5.216%	$54.565	$54.57	$54.55	$54.60
Purchase #6	$208.62	3.491%	$215.9029	$215.90	$215.90	$215.90
Purchase #7	$18.41	5.211%	$19.3693	$19.37	$19.35	$19.40
7 purchase totals =	$696.50		$755.6385	$755.65	$755.60	$755.80