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	$154.63	13.733%	$175.8653	$175.87	$175.85	$175.90
Purchase #2	$162.61	7.372%	$174.5976	$174.60	$174.60	$174.60
Purchase #3	$126.26	13.697%	$143.5538	$143.55	$143.55	$143.60
Purchase #4	$175.88	4.862%	$184.4313	$184.43	$184.45	$184.40
Purchase #5	$125.65	10.833%	$139.2617	$139.26	$139.25	$139.30
Purchase #6	$35.71	8.286%	$38.6689	$38.67	$38.65	$38.70
Purchase #7	$78.63	13.480%	$89.2293	$89.23	$89.25	$89.20
7 purchase totals =	$859.37		$945.6079	$945.61	$945.60	$945.70