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	$54.40	10.259%	$59.9809	$59.98	$60.00	$60.00
Purchase #2	$34.48	11.124%	$38.3156	$38.32	$38.30	$38.30
Purchase #3	$40.98	3.715%	$42.5024	$42.50	$42.50	$42.50
Purchase #4	$148.62	4.539%	$155.3659	$155.37	$155.35	$155.40
Purchase #5	$136.47	13.299%	$154.6191	$154.62	$154.60	$154.60
Purchase #6	$54.46	5.391%	$57.3959	$57.40	$57.40	$57.40
Purchase #7	$115.77	3.545%	$119.874	$119.87	$119.85	$119.90
7 purchase totals =	$585.18		$628.0538	$628.06	$628.00	$628.10