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	$8.36	6.491%	$8.9026	$8.90	$8.90	$8.90
Purchase #2	$109.32	3.656%	$113.3167	$113.32	$113.30	$113.30
Purchase #3	$151.33	8.673%	$164.4549	$164.45	$164.45	$164.50
Purchase #4	$66.81	9.771%	$73.338	$73.34	$73.35	$73.30
Purchase #5	$40.86	4.810%	$42.8254	$42.83	$42.85	$42.80
Purchase #6	$200.42	5.572%	$211.5874	$211.59	$211.60	$211.60
Purchase #7	$141.94	7.652%	$152.8012	$152.80	$152.80	$152.80
7 purchase totals =	$719.04		$767.2262	$767.23	$767.25	$767.20