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	$22.52	3.373%	$23.2796	$23.28	$23.30	$23.30
Purchase #2	$237.50	11.370%	$264.5038	$264.50	$264.50	$264.50
Purchase #3	$53.75	3.209%	$55.4748	$55.47	$55.45	$55.50
Purchase #4	$92.38	6.226%	$98.1316	$98.13	$98.15	$98.10
Purchase #5	$154.43	8.139%	$166.9991	$167.00	$167.00	$167.00
Purchase #6	$82.68	9.584%	$90.6041	$90.60	$90.60	$90.60
Purchase #7	$15.49	8.686%	$16.8355	$16.84	$16.85	$16.80
7 purchase totals =	$658.75		$715.8285	$715.82	$715.85	$715.80