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	$18.61	7.516%	$20.0087	$20.01	$20.00	$20.00
Purchase #2	$40.59	9.569%	$44.4741	$44.47	$44.45	$44.50
Purchase #3	$60.66	3.220%	$62.6133	$62.61	$62.60	$62.60
Purchase #4	$150.59	6.291%	$160.0636	$160.06	$160.05	$160.10
Purchase #5	$72.99	10.689%	$80.7919	$80.79	$80.80	$80.80
Purchase #6	$59.41	4.661%	$62.1791	$62.18	$62.20	$62.20
Purchase #7	$141.42	11.534%	$157.7314	$157.73	$157.75	$157.70
7 purchase totals =	$544.27		$587.8621	$587.85	$587.85	$587.90