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	$118.67	7.828%	$127.9595	$127.96	$127.95	$128.00
Purchase #2	$156.70	12.631%	$176.4928	$176.49	$176.50	$176.50
Purchase #3	$152.92	11.350%	$170.2764	$170.28	$170.30	$170.30
Purchase #4	$207.25	9.172%	$226.259	$226.26	$226.25	$226.30
Purchase #5	$100.41	11.176%	$111.6318	$111.63	$111.65	$111.60
Purchase #6	$6.97	9.464%	$7.6296	$7.63	$7.65	$7.60
Purchase #7	$48.80	3.677%	$50.5944	$50.59	$50.60	$50.60
7 purchase totals =	$791.72		$870.8435	$870.84	$870.90	$870.90