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	$149.92	9.623%	$164.3468	$164.35	$164.35	$164.30
Purchase #2	$34.70	11.598%	$38.7245	$38.72	$38.70	$38.70
Purchase #3	$190.84	12.287%	$214.2885	$214.29	$214.30	$214.30
Purchase #4	$153.86	8.277%	$166.595	$166.60	$166.60	$166.60
Purchase #5	$199.93	4.208%	$208.3431	$208.34	$208.35	$208.30
Purchase #6	$135.72	5.457%	$143.1262	$143.13	$143.15	$143.10
Purchase #7	$65.35	11.516%	$72.8757	$72.88	$72.90	$72.90
7 purchase totals =	$930.32		$1,008.2998	$1,008.31	$1,008.35	$1,008.20