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	$98.72	4.739%	$103.3983	$103.40	$103.40	$103.40
Purchase #2	$165.43	10.376%	$182.595	$182.60	$182.60	$182.60
Purchase #3	$246.82	13.317%	$279.689	$279.69	$279.70	$279.70
Purchase #4	$127.27	8.664%	$138.2967	$138.30	$138.30	$138.30
Purchase #5	$127.51	3.406%	$131.853	$131.85	$131.85	$131.90
Purchase #6	$92.89	12.269%	$104.2867	$104.29	$104.30	$104.30
Purchase #7	$118.90	8.460%	$128.9589	$128.96	$128.95	$129.00
7 purchase totals =	$977.54		$1,069.0776	$1,069.09	$1,069.10	$1,069.20