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	$139.35	8.502%	$151.1975	$151.20	$151.20	$151.20
Purchase #2	$91.29	8.128%	$98.7101	$98.71	$98.70	$98.70
Purchase #3	$106.85	7.197%	$114.54	$114.54	$114.55	$114.50
Purchase #4	$213.54	11.733%	$238.5946	$238.59	$238.60	$238.60
Purchase #5	$74.34	12.234%	$83.4348	$83.43	$83.45	$83.40
Purchase #6	$11.97	12.234%	$13.4344	$13.43	$13.45	$13.40
Purchase #7	$145.29	3.499%	$150.3737	$150.37	$150.35	$150.40
7 purchase totals =	$782.63		$850.2851	$850.27	$850.30	$850.20