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	$94.81	5.434%	$99.962	$99.96	$99.95	$100.00
Purchase #2	$104.32	8.190%	$112.8638	$112.86	$112.85	$112.90
Purchase #3	$34.55	3.143%	$35.6359	$35.64	$35.65	$35.60
Purchase #4	$196.97	11.610%	$219.8382	$219.84	$219.85	$219.80
Purchase #5	$137.51	3.604%	$142.4659	$142.47	$142.45	$142.50
Purchase #6	$248.52	12.325%	$279.1501	$279.15	$279.15	$279.20
Purchase #7	$81.97	9.871%	$90.0613	$90.06	$90.05	$90.10
7 purchase totals =	$898.65		$979.9772	$979.98	$979.95	$980.10