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	$82.50	8.335%	$89.3764	$89.38	$89.40	$89.40
Purchase #2	$157.74	10.339%	$174.0487	$174.05	$174.05	$174.00
Purchase #3	$172.87	11.235%	$192.2919	$192.29	$192.30	$192.30
Purchase #4	$29.36	8.824%	$31.9507	$31.95	$31.95	$32.00
Purchase #5	$155.60	5.643%	$164.3805	$164.38	$164.40	$164.40
Purchase #6	$43.87	10.799%	$48.6075	$48.61	$48.60	$48.60
Purchase #7	$198.45	10.161%	$218.6145	$218.61	$218.60	$218.60
7 purchase totals =	$840.39		$919.2702	$919.27	$919.30	$919.30