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	$132.73	11.739%	$148.3112	$148.31	$148.30	$148.30
Purchase #2	$40.97	10.545%	$45.2903	$45.29	$45.30	$45.30
Purchase #3	$246.59	11.704%	$275.4509	$275.45	$275.45	$275.50
Purchase #4	$42.42	3.465%	$43.8899	$43.89	$43.90	$43.90
Purchase #5	$91.93	11.193%	$102.2197	$102.22	$102.20	$102.20
Purchase #6	$159.83	10.215%	$176.1566	$176.16	$176.15	$176.20
Purchase #7	$15.42	4.228%	$16.072	$16.07	$16.05	$16.10
7 purchase totals =	$729.89		$807.3906	$807.39	$807.35	$807.50