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	$12.26	8.404%	$13.2903	$13.29	$13.30	$13.30
Purchase #2	$43.50	6.346%	$46.2605	$46.26	$46.25	$46.30
Purchase #3	$104.55	13.319%	$118.475	$118.48	$118.50	$118.50
Purchase #4	$167.27	3.105%	$172.4637	$172.46	$172.45	$172.50
Purchase #5	$156.43	10.368%	$172.6487	$172.65	$172.65	$172.60
Purchase #6	$65.60	11.655%	$73.2457	$73.25	$73.25	$73.20
Purchase #7	$249.49	8.161%	$269.8509	$269.85	$269.85	$269.90
7 purchase totals =	$799.10		$866.2348	$866.24	$866.25	$866.30