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	$185.50	10.711%	$205.3689	$205.37	$205.35	$205.40
Purchase #2	$55.96	6.163%	$59.4088	$59.41	$59.40	$59.40
Purchase #3	$29.87	8.858%	$32.5159	$32.52	$32.50	$32.50
Purchase #4	$172.37	3.479%	$178.3668	$178.37	$178.35	$178.40
Purchase #5	$122.50	13.451%	$138.9775	$138.98	$139.00	$139.00
Purchase #6	$146.47	4.686%	$153.3336	$153.33	$153.35	$153.30
Purchase #7	$163.96	4.432%	$171.2267	$171.23	$171.25	$171.20
7 purchase totals =	$876.63		$939.1982	$939.21	$939.20	$939.20