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	$139.95	10.239%	$154.2795	$154.28	$154.30	$154.30
Purchase #2	$231.49	3.181%	$238.8537	$238.85	$238.85	$238.90
Purchase #3	$242.72	5.363%	$255.7371	$255.74	$255.75	$255.70
Purchase #4	$140.72	12.478%	$158.279	$158.28	$158.30	$158.30
Purchase #5	$79.98	3.369%	$82.6745	$82.67	$82.65	$82.70
Purchase #6	$153.47	7.196%	$164.5137	$164.51	$164.50	$164.50
Purchase #7	$16.55	11.709%	$18.4878	$18.49	$18.50	$18.50
7 purchase totals =	$1,004.88		$1,072.8253	$1,072.82	$1,072.85	$1,072.90