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	$132.34	5.167%	$139.178	$139.18	$139.20	$139.20
Purchase #2	$30.71	7.130%	$32.8996	$32.90	$32.90	$32.90
Purchase #3	$98.47	10.116%	$108.4312	$108.43	$108.45	$108.40
Purchase #4	$80.49	8.624%	$87.4315	$87.43	$87.45	$87.40
Purchase #5	$39.34	10.681%	$43.5419	$43.54	$43.55	$43.50
Purchase #6	$84.83	8.313%	$91.8819	$91.88	$91.90	$91.90
Purchase #7	$35.59	12.854%	$40.1647	$40.16	$40.15	$40.20
7 purchase totals =	$501.77		$543.5288	$543.52	$543.60	$543.50