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	$73.71	11.673%	$82.3142	$82.31	$82.30	$82.30
Purchase #2	$78.95	5.281%	$83.1193	$83.12	$83.10	$83.10
Purchase #3	$18.66	13.237%	$21.13	$21.13	$21.15	$21.10
Purchase #4	$213.40	3.544%	$220.9629	$220.96	$220.95	$221.00
Purchase #5	$112.35	5.793%	$118.8584	$118.86	$118.85	$118.90
Purchase #6	$230.82	10.593%	$255.2708	$255.27	$255.25	$255.30
Purchase #7	$30.74	11.205%	$34.1844	$34.18	$34.20	$34.20
7 purchase totals =	$758.63		$815.8400	$815.83	$815.80	$815.90