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	$40.37	12.851%	$45.5579	$45.56	$45.55	$45.60
Purchase #2	$164.89	11.294%	$183.5127	$183.51	$183.50	$183.50
Purchase #3	$67.46	3.152%	$69.5863	$69.59	$69.60	$69.60
Purchase #4	$47.42	12.585%	$53.3878	$53.39	$53.40	$53.40
Purchase #5	$123.86	3.655%	$128.3871	$128.39	$128.40	$128.40
Purchase #6	$52.62	5.326%	$55.4225	$55.42	$55.40	$55.40
Purchase #7	$34.43	4.848%	$36.0992	$36.10	$36.10	$36.10
7 purchase totals =	$531.05		$571.9535	$571.96	$571.95	$572.00