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	$123.66	12.703%	$139.3685	$139.37	$139.35	$139.40
Purchase #2	$159.43	7.685%	$171.6822	$171.68	$171.70	$171.70
Purchase #3	$204.28	8.857%	$222.3731	$222.37	$222.35	$222.40
Purchase #4	$228.86	11.638%	$255.4947	$255.49	$255.50	$255.50
Purchase #5	$118.90	13.398%	$134.8302	$134.83	$134.85	$134.80
Purchase #6	$127.32	11.503%	$141.9656	$141.97	$141.95	$142.00
Purchase #7	$119.94	7.483%	$128.9151	$128.92	$128.90	$128.90
7 purchase totals =	$1,082.39		$1,194.6294	$1,194.63	$1,194.60	$1,194.70