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	$52.92	6.848%	$56.544	$56.54	$56.55	$56.50
Purchase #2	$123.70	8.191%	$133.8323	$133.83	$133.85	$133.80
Purchase #3	$69.50	13.143%	$78.6344	$78.63	$78.65	$78.60
Purchase #4	$196.98	8.495%	$213.7135	$213.71	$213.70	$213.70
Purchase #5	$66.83	7.332%	$71.73	$71.73	$71.75	$71.70
Purchase #6	$198.56	9.680%	$217.7806	$217.78	$217.80	$217.80
Purchase #7	$58.92	13.186%	$66.6892	$66.69	$66.70	$66.70
7 purchase totals =	$767.41		$838.9240	$838.91	$839.00	$838.80