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	$240.77	5.738%	$254.5854	$254.59	$254.60	$254.60
Purchase #2	$158.41	12.146%	$177.6505	$177.65	$177.65	$177.70
Purchase #3	$90.53	10.575%	$100.1035	$100.10	$100.10	$100.10
Purchase #4	$181.44	8.254%	$196.4161	$196.42	$196.40	$196.40
Purchase #5	$146.46	5.738%	$154.8639	$154.86	$154.85	$154.90
Purchase #6	$181.95	5.500%	$191.9573	$191.96	$191.95	$192.00
Purchase #7	$68.29	9.306%	$74.6451	$74.65	$74.65	$74.60
7 purchase totals =	$1,067.85		$1,150.2218	$1,150.23	$1,150.20	$1,150.30