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	$138.61	4.417%	$144.7324	$144.73	$144.75	$144.70
Purchase #2	$249.60	12.587%	$281.0172	$281.02	$281.00	$281.00
Purchase #3	$74.95	10.191%	$82.5882	$82.59	$82.60	$82.60
Purchase #4	$82.94	10.702%	$91.8162	$91.82	$91.80	$91.80
Purchase #5	$159.29	5.848%	$168.6053	$168.61	$168.60	$168.60
Purchase #6	$164.81	11.646%	$184.0038	$184.00	$184.00	$184.00
Purchase #7	$121.45	10.640%	$134.3723	$134.37	$134.35	$134.40
7 purchase totals =	$991.65		$1,087.1354	$1,087.14	$1,087.10	$1,087.10