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	$194.60	11.636%	$217.2437	$217.24	$217.25	$217.20
Purchase #2	$30.47	9.628%	$33.4037	$33.40	$33.40	$33.40
Purchase #3	$103.28	13.443%	$117.1639	$117.16	$117.15	$117.20
Purchase #4	$140.38	11.220%	$156.1306	$156.13	$156.15	$156.10
Purchase #5	$130.59	6.854%	$139.5406	$139.54	$139.55	$139.50
Purchase #6	$137.84	5.528%	$145.4598	$145.46	$145.45	$145.50
Purchase #7	$66.37	9.773%	$72.8563	$72.86	$72.85	$72.90
7 purchase totals =	$803.53		$881.7986	$881.79	$881.80	$881.80