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	$239.65	12.764%	$270.2389	$270.24	$270.25	$270.20
Purchase #2	$12.43	8.314%	$13.4634	$13.46	$13.45	$13.50
Purchase #3	$229.44	11.692%	$256.2661	$256.27	$256.25	$256.30
Purchase #4	$106.31	7.650%	$114.4427	$114.44	$114.45	$114.40
Purchase #5	$104.26	7.257%	$111.8261	$111.83	$111.85	$111.80
Purchase #6	$15.28	3.357%	$15.7929	$15.79	$15.80	$15.80
Purchase #7	$50.48	13.262%	$57.1747	$57.17	$57.15	$57.20
7 purchase totals =	$757.85		$839.2048	$839.20	$839.20	$839.20