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	$218.87	4.361%	$228.4149	$228.41	$228.40	$228.40
Purchase #2	$134.55	10.243%	$148.332	$148.33	$148.35	$148.30
Purchase #3	$138.84	8.167%	$150.1791	$150.18	$150.20	$150.20
Purchase #4	$165.87	3.831%	$172.2245	$172.22	$172.20	$172.20
Purchase #5	$50.38	8.260%	$54.5414	$54.54	$54.55	$54.50
Purchase #6	$69.89	3.827%	$72.5647	$72.56	$72.55	$72.60
Purchase #7	$12.84	13.193%	$14.534	$14.53	$14.55	$14.50
7 purchase totals =	$791.24		$840.7906	$840.77	$840.80	$840.70