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	$237.38	7.755%	$255.7888	$255.79	$255.80	$255.80
Purchase #2	$97.98	4.615%	$102.5018	$102.50	$102.50	$102.50
Purchase #3	$96.64	7.700%	$104.0813	$104.08	$104.10	$104.10
Purchase #4	$241.44	8.635%	$262.2883	$262.29	$262.30	$262.30
Purchase #5	$183.41	7.350%	$196.8906	$196.89	$196.90	$196.90
Purchase #6	$143.27	3.583%	$148.4034	$148.40	$148.40	$148.40
Purchase #7	$45.41	9.714%	$49.8211	$49.82	$49.80	$49.80
7 purchase totals =	$1,045.53		$1,119.7753	$1,119.77	$1,119.80	$1,119.80