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	$136.48	5.720%	$144.2867	$144.29	$144.30	$144.30
Purchase #2	$168.63	11.402%	$187.8572	$187.86	$187.85	$187.90
Purchase #3	$226.60	12.521%	$254.9726	$254.97	$254.95	$255.00
Purchase #4	$113.88	11.874%	$127.4021	$127.40	$127.40	$127.40
Purchase #5	$135.60	5.114%	$142.5346	$142.53	$142.55	$142.50
Purchase #6	$20.37	5.105%	$21.4099	$21.41	$21.40	$21.40
Purchase #7	$230.67	11.796%	$257.8798	$257.88	$257.90	$257.90
7 purchase totals =	$1,032.23		$1,136.3429	$1,136.34	$1,136.35	$1,136.40