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	$33.79	5.667%	$35.7049	$35.70	$35.70	$35.70
Purchase #2	$142.36	9.305%	$155.6066	$155.61	$155.60	$155.60
Purchase #3	$170.52	11.577%	$190.2611	$190.26	$190.25	$190.30
Purchase #4	$249.26	13.484%	$282.8702	$282.87	$282.85	$282.90
Purchase #5	$100.37	11.151%	$111.5623	$111.56	$111.55	$111.60
Purchase #6	$96.42	4.484%	$100.7435	$100.74	$100.75	$100.70
Purchase #7	$34.95	9.236%	$38.178	$38.18	$38.20	$38.20
7 purchase totals =	$827.67		$914.9266	$914.92	$914.90	$915.00