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	$143.86	10.799%	$159.3954	$159.40	$159.40	$159.40
Purchase #2	$39.56	7.685%	$42.6002	$42.60	$42.60	$42.60
Purchase #3	$38.35	11.677%	$42.8281	$42.83	$42.85	$42.80
Purchase #4	$62.54	3.308%	$64.6088	$64.61	$64.60	$64.60
Purchase #5	$156.29	9.121%	$170.5452	$170.55	$170.55	$170.50
Purchase #6	$164.47	13.640%	$186.9037	$186.90	$186.90	$186.90
Purchase #7	$15.68	8.493%	$17.0117	$17.01	$17.00	$17.00
7 purchase totals =	$620.75		$683.8931	$683.90	$683.90	$683.80