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	$137.27	12.658%	$154.6456	$154.65	$154.65	$154.60
Purchase #2	$137.73	5.613%	$145.4608	$145.46	$145.45	$145.50
Purchase #3	$188.40	4.501%	$196.8799	$196.88	$196.90	$196.90
Purchase #4	$92.92	13.344%	$105.3192	$105.32	$105.30	$105.30
Purchase #5	$111.95	9.155%	$122.199	$122.20	$122.20	$122.20
Purchase #6	$107.45	3.246%	$110.9378	$110.94	$110.95	$110.90
Purchase #7	$64.45	13.169%	$72.9374	$72.94	$72.95	$72.90
7 purchase totals =	$840.17		$908.3797	$908.39	$908.40	$908.30