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	$42.90	4.710%	$44.9206	$44.92	$44.90	$44.90
Purchase #2	$42.27	11.256%	$47.0279	$47.03	$47.05	$47.00
Purchase #3	$37.85	7.144%	$40.554	$40.55	$40.55	$40.60
Purchase #4	$206.60	13.564%	$234.6232	$234.62	$234.60	$234.60
Purchase #5	$38.96	3.313%	$40.2507	$40.25	$40.25	$40.30
Purchase #6	$64.41	11.212%	$71.6316	$71.63	$71.65	$71.60
Purchase #7	$114.97	12.133%	$128.9193	$128.92	$128.90	$128.90
7 purchase totals =	$547.96		$607.9273	$607.92	$607.90	$607.90