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	$43.31	11.868%	$48.45	$48.45	$48.45	$48.50
Purchase #2	$148.45	4.292%	$154.8215	$154.82	$154.80	$154.80
Purchase #3	$102.54	6.560%	$109.2666	$109.27	$109.25	$109.30
Purchase #4	$66.54	11.376%	$74.1096	$74.11	$74.10	$74.10
Purchase #5	$136.91	11.283%	$152.3576	$152.36	$152.35	$152.40
Purchase #6	$139.37	11.654%	$155.6122	$155.61	$155.60	$155.60
Purchase #7	$140.78	5.136%	$148.0105	$148.01	$148.00	$148.00
7 purchase totals =	$777.90		$842.6280	$842.63	$842.55	$842.70