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	$102.40	12.495%	$115.1949	$115.19	$115.20	$115.20
Purchase #2	$154.57	11.601%	$172.5017	$172.50	$172.50	$172.50
Purchase #3	$174.45	9.740%	$191.4414	$191.44	$191.45	$191.40
Purchase #4	$160.99	11.133%	$178.913	$178.91	$178.90	$178.90
Purchase #5	$163.60	12.522%	$184.086	$184.09	$184.10	$184.10
Purchase #6	$119.86	10.368%	$132.2871	$132.29	$132.30	$132.30
Purchase #7	$43.76	4.772%	$45.8482	$45.85	$45.85	$45.80
7 purchase totals =	$919.63		$1,020.2723	$1,020.27	$1,020.30	$1,020.20