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	$40.49	10.126%	$44.59	$44.59	$44.60	$44.60
Purchase #2	$160.83	12.696%	$181.249	$181.25	$181.25	$181.20
Purchase #3	$42.52	10.170%	$46.8443	$46.84	$46.85	$46.80
Purchase #4	$20.89	7.195%	$22.393	$22.39	$22.40	$22.40
Purchase #5	$56.60	7.829%	$61.0312	$61.03	$61.05	$61.00
Purchase #6	$145.56	12.331%	$163.509	$163.51	$163.50	$163.50
Purchase #7	$191.61	4.826%	$200.8571	$200.86	$200.85	$200.90
7 purchase totals =	$658.50		$720.4736	$720.47	$720.50	$720.40