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	$220.35	8.412%	$238.8858	$238.89	$238.90	$238.90
Purchase #2	$205.99	9.153%	$224.8443	$224.84	$224.85	$224.80
Purchase #3	$35.55	10.462%	$39.2692	$39.27	$39.25	$39.30
Purchase #4	$126.54	12.158%	$141.9247	$141.92	$141.90	$141.90
Purchase #5	$230.73	12.805%	$260.275	$260.28	$260.30	$260.30
Purchase #6	$80.91	11.732%	$90.4024	$90.40	$90.40	$90.40
Purchase #7	$10.93	6.105%	$11.5973	$11.60	$11.60	$11.60
7 purchase totals =	$911.00		$1,007.1987	$1,007.20	$1,007.20	$1,007.20