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	$218.71	6.351%	$232.6003	$232.60	$232.60	$232.60
Purchase #2	$30.82	13.842%	$35.0861	$35.09	$35.10	$35.10
Purchase #3	$143.27	3.858%	$148.7974	$148.80	$148.80	$148.80
Purchase #4	$52.55	13.184%	$59.4782	$59.48	$59.50	$59.50
Purchase #5	$55.95	9.517%	$61.2748	$61.27	$61.25	$61.30
Purchase #6	$157.56	9.790%	$172.9851	$172.99	$173.00	$173.00
Purchase #7	$130.96	10.660%	$144.9203	$144.92	$144.90	$144.90
7 purchase totals =	$789.82		$855.1422	$855.15	$855.15	$855.20