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	$154.64	12.566%	$174.0721	$174.07	$174.05	$174.10
Purchase #2	$171.56	11.267%	$190.8897	$190.89	$190.90	$190.90
Purchase #3	$108.90	5.679%	$115.0844	$115.08	$115.10	$115.10
Purchase #4	$87.82	3.105%	$90.5468	$90.55	$90.55	$90.50
Purchase #5	$152.42	6.648%	$162.5529	$162.55	$162.55	$162.60
Purchase #6	$172.86	7.372%	$185.6032	$185.60	$185.60	$185.60
Purchase #7	$52.99	7.620%	$57.0278	$57.03	$57.05	$57.00
7 purchase totals =	$901.19		$975.7769	$975.77	$975.80	$975.80