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	$239.84	13.550%	$272.3383	$272.34	$272.35	$272.30
Purchase #2	$151.80	13.817%	$172.7742	$172.77	$172.75	$172.80
Purchase #3	$114.38	10.496%	$126.3853	$126.39	$126.40	$126.40
Purchase #4	$211.99	12.650%	$238.8067	$238.81	$238.80	$238.80
Purchase #5	$185.78	5.570%	$196.1279	$196.13	$196.15	$196.10
Purchase #6	$241.49	3.677%	$250.3696	$250.37	$250.35	$250.40
Purchase #7	$23.30	5.423%	$24.5636	$24.56	$24.55	$24.60
7 purchase totals =	$1,168.58		$1,281.3656	$1,281.37	$1,281.35	$1,281.40