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	$224.81	7.277%	$241.1694	$241.17	$241.15	$241.20
Purchase #2	$91.57	10.116%	$100.8332	$100.83	$100.85	$100.80
Purchase #3	$24.82	12.105%	$27.8245	$27.82	$27.80	$27.80
Purchase #4	$156.48	12.575%	$176.1574	$176.16	$176.15	$176.20
Purchase #5	$113.31	10.399%	$125.0931	$125.09	$125.10	$125.10
Purchase #6	$104.43	11.846%	$116.8008	$116.80	$116.80	$116.80
Purchase #7	$88.89	10.706%	$98.4066	$98.41	$98.40	$98.40
7 purchase totals =	$804.31		$886.2850	$886.28	$886.25	$886.30