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	$98.78	5.508%	$104.2208	$104.22	$104.20	$104.20
Purchase #2	$104.78	4.627%	$109.6282	$109.63	$109.65	$109.60
Purchase #3	$38.61	7.809%	$41.6251	$41.63	$41.65	$41.60
Purchase #4	$227.90	12.156%	$255.6035	$255.60	$255.60	$255.60
Purchase #5	$92.51	8.439%	$100.3169	$100.32	$100.30	$100.30
Purchase #6	$82.87	9.364%	$90.6299	$90.63	$90.65	$90.60
Purchase #7	$243.51	4.653%	$254.8405	$254.84	$254.85	$254.80
7 purchase totals =	$888.96		$956.8649	$956.87	$956.90	$956.70