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	$197.83	9.380%	$216.3865	$216.39	$216.40	$216.40
Purchase #2	$233.48	3.496%	$241.6425	$241.64	$241.65	$241.60
Purchase #3	$131.56	9.105%	$143.5385	$143.54	$143.55	$143.50
Purchase #4	$146.25	12.437%	$164.4391	$164.44	$164.45	$164.40
Purchase #5	$40.45	13.222%	$45.7983	$45.80	$45.80	$45.80
Purchase #6	$131.28	10.714%	$145.3453	$145.35	$145.35	$145.30
Purchase #7	$234.71	12.223%	$263.3986	$263.40	$263.40	$263.40
7 purchase totals =	$1,115.56		$1,220.5488	$1,220.56	$1,220.60	$1,220.40