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	$77.44	7.838%	$83.5097	$83.51	$83.50	$83.50
Purchase #2	$52.78	8.858%	$57.4553	$57.46	$57.45	$57.50
Purchase #3	$245.59	4.171%	$255.8336	$255.83	$255.85	$255.80
Purchase #4	$115.62	10.553%	$127.8214	$127.82	$127.80	$127.80
Purchase #5	$57.54	10.867%	$63.7929	$63.79	$63.80	$63.80
Purchase #6	$64.71	10.595%	$71.566	$71.57	$71.55	$71.60
Purchase #7	$121.83	4.391%	$127.1796	$127.18	$127.20	$127.20
7 purchase totals =	$735.51		$787.1585	$787.16	$787.15	$787.20