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	$25.34	3.596%	$26.2512	$26.25	$26.25	$26.30
Purchase #2	$97.83	7.789%	$105.45	$105.45	$105.45	$105.50
Purchase #3	$81.39	11.302%	$90.5887	$90.59	$90.60	$90.60
Purchase #4	$166.31	6.316%	$176.8141	$176.81	$176.80	$176.80
Purchase #5	$128.78	5.695%	$136.114	$136.11	$136.10	$136.10
Purchase #6	$127.39	11.839%	$142.4717	$142.47	$142.45	$142.50
Purchase #7	$14.54	8.743%	$15.8112	$15.81	$15.80	$15.80
7 purchase totals =	$641.58		$693.5009	$693.49	$693.45	$693.60