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	$103.66	9.447%	$113.4528	$113.45	$113.45	$113.50
Purchase #2	$114.62	8.359%	$124.2011	$124.20	$124.20	$124.20
Purchase #3	$184.82	8.221%	$200.0141	$200.01	$200.00	$200.00
Purchase #4	$190.90	5.116%	$200.6664	$200.67	$200.65	$200.70
Purchase #5	$178.89	6.555%	$190.6162	$190.62	$190.60	$190.60
Purchase #6	$72.33	8.347%	$78.3674	$78.37	$78.35	$78.40
Purchase #7	$78.81	4.343%	$82.2327	$82.23	$82.25	$82.20
7 purchase totals =	$924.03		$989.5507	$989.55	$989.50	$989.60