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	$11.72	4.450%	$12.2415	$12.24	$12.25	$12.20
Purchase #2	$250.62	12.671%	$282.3761	$282.38	$282.40	$282.40
Purchase #3	$164.61	13.271%	$186.4554	$186.46	$186.45	$186.50
Purchase #4	$149.58	8.478%	$162.2614	$162.26	$162.25	$162.30
Purchase #5	$12.76	11.619%	$14.2426	$14.24	$14.25	$14.20
Purchase #6	$134.54	13.307%	$152.4432	$152.44	$152.45	$152.40
Purchase #7	$123.47	3.291%	$127.5334	$127.53	$127.55	$127.50
7 purchase totals =	$847.30		$937.5536	$937.55	$937.60	$937.50