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	$43.83	5.857%	$46.3971	$46.40	$46.40	$46.40
Purchase #2	$161.92	4.741%	$169.5966	$169.60	$169.60	$169.60
Purchase #3	$161.81	13.458%	$183.5864	$183.59	$183.60	$183.60
Purchase #4	$136.85	7.685%	$147.3669	$147.37	$147.35	$147.40
Purchase #5	$212.39	12.167%	$238.2315	$238.23	$238.25	$238.20
Purchase #6	$86.40	6.109%	$91.6782	$91.68	$91.70	$91.70
Purchase #7	$113.86	8.117%	$123.102	$123.10	$123.10	$123.10
7 purchase totals =	$917.06		$999.9587	$999.97	$1,000.00	$1,000.00