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	$176.60	13.729%	$200.8454	$200.85	$200.85	$200.80
Purchase #2	$43.87	3.295%	$45.3155	$45.32	$45.30	$45.30
Purchase #3	$167.93	10.443%	$185.4669	$185.47	$185.45	$185.50
Purchase #4	$80.94	3.246%	$83.5673	$83.57	$83.55	$83.60
Purchase #5	$117.53	5.253%	$123.7039	$123.70	$123.70	$123.70
Purchase #6	$214.63	8.220%	$232.2726	$232.27	$232.25	$232.30
Purchase #7	$41.96	12.401%	$47.1635	$47.16	$47.15	$47.20
7 purchase totals =	$843.46		$918.3351	$918.34	$918.25	$918.40