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	$247.80	13.561%	$281.4042	$281.40	$281.40	$281.40
Purchase #2	$7.58	10.768%	$8.3962	$8.40	$8.40	$8.40
Purchase #3	$39.88	11.379%	$44.4179	$44.42	$44.40	$44.40
Purchase #4	$178.27	10.386%	$196.7851	$196.79	$196.80	$196.80
Purchase #5	$201.55	11.455%	$224.6376	$224.64	$224.65	$224.60
Purchase #6	$65.82	10.288%	$72.5916	$72.59	$72.60	$72.60
Purchase #7	$38.47	13.688%	$43.7358	$43.74	$43.75	$43.70
7 purchase totals =	$779.37		$871.9684	$871.98	$872.00	$871.90