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	$139.53	6.431%	$148.5032	$148.50	$148.50	$148.50
Purchase #2	$219.79	11.231%	$244.4746	$244.47	$244.45	$244.50
Purchase #3	$160.26	9.138%	$174.9046	$174.90	$174.90	$174.90
Purchase #4	$113.71	3.427%	$117.6068	$117.61	$117.60	$117.60
Purchase #5	$145.52	5.182%	$153.0608	$153.06	$153.05	$153.10
Purchase #6	$198.64	12.715%	$223.8971	$223.90	$223.90	$223.90
Purchase #7	$112.45	5.300%	$118.4099	$118.41	$118.40	$118.40
7 purchase totals =	$1,089.90		$1,180.8570	$1,180.85	$1,180.80	$1,180.90