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	$44.82	8.407%	$48.588	$48.59	$48.60	$48.60
Purchase #2	$106.62	9.233%	$116.4642	$116.46	$116.45	$116.50
Purchase #3	$52.54	4.863%	$55.095	$55.10	$55.10	$55.10
Purchase #4	$114.99	11.676%	$128.4162	$128.42	$128.40	$128.40
Purchase #5	$192.58	10.321%	$212.4562	$212.46	$212.45	$212.50
Purchase #6	$55.81	11.290%	$62.1109	$62.11	$62.10	$62.10
Purchase #7	$41.68	13.594%	$47.346	$47.35	$47.35	$47.30
7 purchase totals =	$609.04		$670.4765	$670.49	$670.45	$670.50