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	$136.52	11.715%	$152.5133	$152.51	$152.50	$152.50
Purchase #2	$49.34	13.698%	$56.0986	$56.10	$56.10	$56.10
Purchase #3	$131.25	6.357%	$139.5936	$139.59	$139.60	$139.60
Purchase #4	$198.79	3.693%	$206.1313	$206.13	$206.15	$206.10
Purchase #5	$166.70	7.111%	$178.554	$178.55	$178.55	$178.60
Purchase #6	$224.39	5.543%	$236.8279	$236.83	$236.85	$236.80
Purchase #7	$67.46	7.206%	$72.3212	$72.32	$72.30	$72.30
7 purchase totals =	$974.45		$1,042.0399	$1,042.03	$1,042.05	$1,042.00