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	$98.43	10.779%	$109.0398	$109.04	$109.05	$109.00
Purchase #2	$115.29	10.617%	$127.5303	$127.53	$127.55	$127.50
Purchase #3	$41.35	9.286%	$45.1898	$45.19	$45.20	$45.20
Purchase #4	$93.71	12.594%	$105.5118	$105.51	$105.50	$105.50
Purchase #5	$114.84	12.725%	$129.4534	$129.45	$129.45	$129.50
Purchase #6	$63.27	7.564%	$68.0557	$68.06	$68.05	$68.10
Purchase #7	$34.40	3.649%	$35.6553	$35.66	$35.65	$35.70
7 purchase totals =	$561.29		$620.4361	$620.44	$620.45	$620.50