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	$134.88	3.360%	$139.412	$139.41	$139.40	$139.40
Purchase #2	$92.75	8.247%	$100.3991	$100.40	$100.40	$100.40
Purchase #3	$49.47	10.171%	$54.5016	$54.50	$54.50	$54.50
Purchase #4	$23.97	13.399%	$27.1817	$27.18	$27.20	$27.20
Purchase #5	$61.68	11.576%	$68.8201	$68.82	$68.80	$68.80
Purchase #6	$33.80	12.324%	$37.9655	$37.97	$37.95	$38.00
Purchase #7	$109.53	12.545%	$123.2705	$123.27	$123.25	$123.30
7 purchase totals =	$506.08		$551.5505	$551.55	$551.50	$551.60