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	$142.44	6.795%	$152.1188	$152.12	$152.10	$152.10
Purchase #2	$113.59	9.680%	$124.5855	$124.59	$124.60	$124.60
Purchase #3	$131.83	10.269%	$145.3676	$145.37	$145.35	$145.40
Purchase #4	$197.41	11.839%	$220.7814	$220.78	$220.80	$220.80
Purchase #5	$219.63	6.739%	$234.4309	$234.43	$234.45	$234.40
Purchase #6	$218.93	13.644%	$248.8008	$248.80	$248.80	$248.80
Purchase #7	$112.41	9.863%	$123.497	$123.50	$123.50	$123.50
7 purchase totals =	$1,136.24		$1,249.5820	$1,249.59	$1,249.60	$1,249.60