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	$34.27	6.543%	$36.5123	$36.51	$36.50	$36.50
Purchase #2	$37.59	7.443%	$40.3878	$40.39	$40.40	$40.40
Purchase #3	$40.54	12.814%	$45.7348	$45.73	$45.75	$45.70
Purchase #4	$223.39	3.182%	$230.4983	$230.50	$230.50	$230.50
Purchase #5	$7.28	9.232%	$7.9521	$7.95	$7.95	$8.00
Purchase #6	$32.44	12.770%	$36.5826	$36.58	$36.60	$36.60
Purchase #7	$243.32	5.873%	$257.6102	$257.61	$257.60	$257.60
7 purchase totals =	$618.83		$655.2781	$655.27	$655.30	$655.30