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	$57.36	6.449%	$61.0591	$61.06	$61.05	$61.10
Purchase #2	$70.66	8.668%	$76.7848	$76.78	$76.80	$76.80
Purchase #3	$23.98	6.171%	$25.4598	$25.46	$25.45	$25.50
Purchase #4	$70.43	10.516%	$77.8364	$77.84	$77.85	$77.80
Purchase #5	$108.80	11.766%	$121.6014	$121.60	$121.60	$121.60
Purchase #6	$80.32	12.724%	$90.5399	$90.54	$90.55	$90.50
Purchase #7	$103.28	7.676%	$111.2078	$111.21	$111.20	$111.20
7 purchase totals =	$514.83		$564.4892	$564.49	$564.50	$564.50