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	$74.68	10.224%	$82.3153	$82.32	$82.30	$82.30
Purchase #2	$109.31	3.867%	$113.537	$113.54	$113.55	$113.50
Purchase #3	$233.56	9.849%	$256.5633	$256.56	$256.55	$256.60
Purchase #4	$101.97	12.317%	$114.5296	$114.53	$114.55	$114.50
Purchase #5	$53.90	4.726%	$56.4473	$56.45	$56.45	$56.40
Purchase #6	$143.68	3.212%	$148.295	$148.30	$148.30	$148.30
Purchase #7	$33.83	12.442%	$38.0391	$38.04	$38.05	$38.00
7 purchase totals =	$750.93		$809.7266	$809.74	$809.75	$809.60