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	$9.44	13.744%	$10.7374	$10.74	$10.75	$10.70
Purchase #2	$167.54	6.646%	$178.6747	$178.67	$178.65	$178.70
Purchase #3	$82.52	8.556%	$89.5804	$89.58	$89.60	$89.60
Purchase #4	$74.28	8.269%	$80.4222	$80.42	$80.40	$80.40
Purchase #5	$148.78	10.838%	$164.9048	$164.90	$164.90	$164.90
Purchase #6	$178.62	12.349%	$200.6778	$200.68	$200.70	$200.70
Purchase #7	$95.71	7.485%	$102.8739	$102.87	$102.85	$102.90
7 purchase totals =	$756.89		$827.8712	$827.86	$827.85	$827.90