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	$158.35	9.460%	$173.3299	$173.33	$173.35	$173.30
Purchase #2	$204.58	11.381%	$227.8632	$227.86	$227.85	$227.90
Purchase #3	$151.60	11.805%	$169.4964	$169.50	$169.50	$169.50
Purchase #4	$172.82	3.197%	$178.3451	$178.35	$178.35	$178.30
Purchase #5	$21.34	10.868%	$23.6592	$23.66	$23.65	$23.70
Purchase #6	$137.62	6.709%	$146.8529	$146.85	$146.85	$146.90
Purchase #7	$148.25	12.497%	$166.7768	$166.78	$166.80	$166.80
7 purchase totals =	$994.56		$1,086.3235	$1,086.33	$1,086.35	$1,086.40