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	$32.54	3.783%	$33.771	$33.77	$33.75	$33.80
Purchase #2	$101.98	10.348%	$112.5329	$112.53	$112.55	$112.50
Purchase #3	$190.59	12.428%	$214.2765	$214.28	$214.30	$214.30
Purchase #4	$138.70	4.384%	$144.7806	$144.78	$144.80	$144.80
Purchase #5	$159.30	7.320%	$170.9608	$170.96	$170.95	$171.00
Purchase #6	$7.29	3.156%	$7.5201	$7.52	$7.50	$7.50
Purchase #7	$137.59	9.369%	$150.4808	$150.48	$150.50	$150.50
7 purchase totals =	$767.99		$834.3227	$834.32	$834.35	$834.40