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	$238.82	11.628%	$266.59	$266.59	$266.60	$266.60
Purchase #2	$169.92	10.107%	$187.0938	$187.09	$187.10	$187.10
Purchase #3	$85.55	4.381%	$89.2979	$89.30	$89.30	$89.30
Purchase #4	$168.38	7.714%	$181.3688	$181.37	$181.35	$181.40
Purchase #5	$18.84	11.782%	$21.0597	$21.06	$21.05	$21.10
Purchase #6	$246.68	5.568%	$260.4151	$260.42	$260.40	$260.40
Purchase #7	$42.28	5.759%	$44.7149	$44.71	$44.70	$44.70
7 purchase totals =	$970.47		$1,050.5402	$1,050.54	$1,050.50	$1,050.60