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	$135.53	3.642%	$140.466	$140.47	$140.45	$140.50
Purchase #2	$135.73	5.694%	$143.4585	$143.46	$143.45	$143.50
Purchase #3	$180.35	6.816%	$192.6427	$192.64	$192.65	$192.60
Purchase #4	$135.30	13.693%	$153.8266	$153.83	$153.85	$153.80
Purchase #5	$101.39	8.154%	$109.6573	$109.66	$109.65	$109.70
Purchase #6	$89.76	10.863%	$99.5106	$99.51	$99.50	$99.50
Purchase #7	$155.31	9.478%	$170.0303	$170.03	$170.05	$170.00
7 purchase totals =	$933.37		$1,009.5920	$1,009.60	$1,009.60	$1,009.60