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	$72.25	11.244%	$80.3738	$80.37	$80.35	$80.40
Purchase #2	$128.40	7.377%	$137.8721	$137.87	$137.85	$137.90
Purchase #3	$90.59	12.594%	$101.9989	$102.00	$102.00	$102.00
Purchase #4	$250.71	6.255%	$266.3919	$266.39	$266.40	$266.40
Purchase #5	$129.73	7.347%	$139.2613	$139.26	$139.25	$139.30
Purchase #6	$199.81	8.734%	$217.2614	$217.26	$217.25	$217.30
Purchase #7	$111.26	10.774%	$123.2472	$123.25	$123.25	$123.20
7 purchase totals =	$982.75		$1,066.4066	$1,066.40	$1,066.35	$1,066.50