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	$38.86	12.738%	$43.81	$43.81	$43.80	$43.80
Purchase #2	$230.94	8.390%	$250.3159	$250.32	$250.30	$250.30
Purchase #3	$78.82	9.591%	$86.3796	$86.38	$86.40	$86.40
Purchase #4	$105.88	6.349%	$112.6023	$112.60	$112.60	$112.60
Purchase #5	$114.79	13.646%	$130.4542	$130.45	$130.45	$130.50
Purchase #6	$109.82	5.341%	$115.6855	$115.69	$115.70	$115.70
Purchase #7	$232.56	7.765%	$250.6183	$250.62	$250.60	$250.60
7 purchase totals =	$911.67		$989.8658	$989.87	$989.85	$989.90