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	$159.69	5.546%	$168.5464	$168.55	$168.55	$168.50
Purchase #2	$162.80	10.344%	$179.64	$179.64	$179.65	$179.60
Purchase #3	$249.31	8.642%	$270.8554	$270.86	$270.85	$270.90
Purchase #4	$63.47	7.397%	$68.1649	$68.16	$68.15	$68.20
Purchase #5	$202.85	6.255%	$215.5383	$215.54	$215.55	$215.50
Purchase #6	$118.34	8.739%	$128.6817	$128.68	$128.70	$128.70
Purchase #7	$103.77	7.128%	$111.1667	$111.17	$111.15	$111.20
7 purchase totals =	$1,060.23		$1,142.5934	$1,142.60	$1,142.60	$1,142.60