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	$128.78	10.615%	$142.45	$142.45	$142.45	$142.50
Purchase #2	$106.55	3.675%	$110.4657	$110.47	$110.45	$110.50
Purchase #3	$13.83	11.694%	$15.4473	$15.45	$15.45	$15.40
Purchase #4	$96.78	13.532%	$109.8763	$109.88	$109.90	$109.90
Purchase #5	$250.27	8.695%	$272.031	$272.03	$272.05	$272.00
Purchase #6	$109.43	4.605%	$114.4693	$114.47	$114.45	$114.50
Purchase #7	$68.43	13.225%	$77.4799	$77.48	$77.50	$77.50
7 purchase totals =	$774.07		$842.2195	$842.23	$842.25	$842.30