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	$141.52	13.368%	$160.4384	$160.44	$160.45	$160.40
Purchase #2	$193.42	3.536%	$200.2593	$200.26	$200.25	$200.30
Purchase #3	$69.90	9.622%	$76.6258	$76.63	$76.65	$76.60
Purchase #4	$164.81	9.515%	$180.4917	$180.49	$180.50	$180.50
Purchase #5	$15.72	13.565%	$17.8524	$17.85	$17.85	$17.90
Purchase #6	$123.28	13.244%	$139.6072	$139.61	$139.60	$139.60
Purchase #7	$228.56	11.690%	$255.2787	$255.28	$255.30	$255.30
7 purchase totals =	$937.21		$1,030.5535	$1,030.56	$1,030.60	$1,030.60