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	$248.61	12.590%	$279.91	$279.91	$279.90	$279.90
Purchase #2	$164.80	11.580%	$183.8838	$183.88	$183.90	$183.90
Purchase #3	$67.81	10.396%	$74.8595	$74.86	$74.85	$74.90
Purchase #4	$18.69	11.729%	$20.8822	$20.88	$20.90	$20.90
Purchase #5	$124.35	3.296%	$128.4486	$128.45	$128.45	$128.40
Purchase #6	$208.50	5.656%	$220.2928	$220.29	$220.30	$220.30
Purchase #7	$106.62	5.116%	$112.0747	$112.07	$112.05	$112.10
7 purchase totals =	$939.38		$1,020.3516	$1,020.34	$1,020.35	$1,020.40