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	$59.99	8.318%	$64.98	$64.98	$65.00	$65.00
Purchase #2	$201.54	11.255%	$224.2233	$224.22	$224.20	$224.20
Purchase #3	$190.88	12.784%	$215.2821	$215.28	$215.30	$215.30
Purchase #4	$185.66	12.137%	$208.1936	$208.19	$208.20	$208.20
Purchase #5	$74.89	9.585%	$82.0682	$82.07	$82.05	$82.10
Purchase #6	$64.57	10.861%	$71.5829	$71.58	$71.60	$71.60
Purchase #7	$105.68	6.474%	$112.5217	$112.52	$112.50	$112.50
7 purchase totals =	$883.21		$978.8518	$978.84	$978.85	$978.90