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	$137.96	3.741%	$143.1211	$143.12	$143.10	$143.10
Purchase #2	$64.71	3.272%	$66.8273	$66.83	$66.85	$66.80
Purchase #3	$94.83	13.395%	$107.5325	$107.53	$107.55	$107.50
Purchase #4	$197.53	6.733%	$210.8297	$210.83	$210.85	$210.80
Purchase #5	$73.95	10.328%	$81.5876	$81.59	$81.60	$81.60
Purchase #6	$78.72	5.697%	$83.2047	$83.20	$83.20	$83.20
Purchase #7	$140.53	11.282%	$156.3846	$156.38	$156.40	$156.40
7 purchase totals =	$788.23		$849.4875	$849.48	$849.55	$849.40