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	$17.67	4.126%	$18.3991	$18.40	$18.40	$18.40
Purchase #2	$10.76	6.149%	$11.4216	$11.42	$11.40	$11.40
Purchase #3	$18.60	12.176%	$20.8647	$20.86	$20.85	$20.90
Purchase #4	$105.45	7.558%	$113.4199	$113.42	$113.40	$113.40
Purchase #5	$157.38	7.742%	$169.5644	$169.56	$169.55	$169.60
Purchase #6	$61.64	13.758%	$70.1204	$70.12	$70.10	$70.10
Purchase #7	$147.94	3.292%	$152.8102	$152.81	$152.80	$152.80
7 purchase totals =	$519.44		$556.6003	$556.59	$556.50	$556.60