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	$7.78	6.542%	$8.289	$8.29	$8.30	$8.30
Purchase #2	$37.39	5.850%	$39.5773	$39.58	$39.60	$39.60
Purchase #3	$143.27	3.555%	$148.3632	$148.36	$148.35	$148.40
Purchase #4	$79.54	5.349%	$83.7946	$83.79	$83.80	$83.80
Purchase #5	$185.99	7.785%	$200.4693	$200.47	$200.45	$200.50
Purchase #6	$127.93	13.678%	$145.4283	$145.43	$145.45	$145.40
Purchase #7	$174.50	10.561%	$192.9289	$192.93	$192.95	$192.90
7 purchase totals =	$756.40		$818.8506	$818.85	$818.90	$818.90