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	$135.47	5.622%	$143.0861	$143.09	$143.10	$143.10
Purchase #2	$211.82	6.249%	$225.0566	$225.06	$225.05	$225.10
Purchase #3	$216.60	5.842%	$229.2538	$229.25	$229.25	$229.30
Purchase #4	$92.41	11.800%	$103.3144	$103.31	$103.30	$103.30
Purchase #5	$31.89	10.353%	$35.1916	$35.19	$35.20	$35.20
Purchase #6	$242.78	5.784%	$256.8224	$256.82	$256.80	$256.80
Purchase #7	$60.29	7.337%	$64.7135	$64.71	$64.70	$64.70
7 purchase totals =	$991.26		$1,057.4384	$1,057.43	$1,057.40	$1,057.50