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	$70.68	11.578%	$78.8633	$78.86	$78.85	$78.90
Purchase #2	$87.25	3.351%	$90.1737	$90.17	$90.15	$90.20
Purchase #3	$224.37	5.388%	$236.4591	$236.46	$236.45	$236.50
Purchase #4	$101.47	13.524%	$115.1928	$115.19	$115.20	$115.20
Purchase #5	$86.61	5.534%	$91.403	$91.40	$91.40	$91.40
Purchase #6	$59.77	4.492%	$62.4549	$62.45	$62.45	$62.50
Purchase #7	$135.85	13.671%	$154.4221	$154.42	$154.40	$154.40
7 purchase totals =	$766.00		$828.9689	$828.95	$828.90	$829.10