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	$28.28	11.684%	$31.5842	$31.58	$31.60	$31.60
Purchase #2	$64.97	4.578%	$67.9443	$67.94	$67.95	$67.90
Purchase #3	$153.63	12.666%	$173.0888	$173.09	$173.10	$173.10
Purchase #4	$250.65	6.815%	$267.7318	$267.73	$267.75	$267.70
Purchase #5	$105.41	10.210%	$116.1724	$116.17	$116.15	$116.20
Purchase #6	$28.69	12.124%	$32.1684	$32.17	$32.15	$32.20
Purchase #7	$98.75	13.264%	$111.8482	$111.85	$111.85	$111.80
7 purchase totals =	$730.38		$800.5381	$800.53	$800.55	$800.50