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	$105.33	5.611%	$111.2401	$111.24	$111.25	$111.20
Purchase #2	$89.51	6.277%	$95.1285	$95.13	$95.15	$95.10
Purchase #3	$234.80	9.788%	$257.7822	$257.78	$257.80	$257.80
Purchase #4	$61.50	7.874%	$66.3425	$66.34	$66.35	$66.30
Purchase #5	$59.25	7.659%	$63.788	$63.79	$63.80	$63.80
Purchase #6	$73.72	8.597%	$80.0577	$80.06	$80.05	$80.10
Purchase #7	$17.51	3.117%	$18.0558	$18.06	$18.05	$18.10
7 purchase totals =	$641.62		$692.3948	$692.40	$692.45	$692.40