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	$40.63	12.296%	$45.6259	$45.63	$45.65	$45.60
Purchase #2	$101.59	11.613%	$113.3876	$113.39	$113.40	$113.40
Purchase #3	$38.41	9.738%	$42.1504	$42.15	$42.15	$42.20
Purchase #4	$116.79	9.151%	$127.4775	$127.48	$127.50	$127.50
Purchase #5	$7.31	12.629%	$8.2332	$8.23	$8.25	$8.20
Purchase #6	$117.92	9.594%	$129.2332	$129.23	$129.25	$129.20
Purchase #7	$22.96	9.820%	$25.2147	$25.21	$25.20	$25.20
7 purchase totals =	$445.61		$491.3225	$491.32	$491.40	$491.30