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	$15.68	11.694%	$17.5136	$17.51	$17.50	$17.50
Purchase #2	$166.31	9.128%	$181.4908	$181.49	$181.50	$181.50
Purchase #3	$176.43	5.337%	$185.8461	$185.85	$185.85	$185.80
Purchase #4	$100.63	7.858%	$108.5375	$108.54	$108.55	$108.50
Purchase #5	$33.34	12.457%	$37.4932	$37.49	$37.50	$37.50
Purchase #6	$248.31	8.143%	$268.5299	$268.53	$268.55	$268.50
Purchase #7	$106.78	8.524%	$115.8819	$115.88	$115.90	$115.90
7 purchase totals =	$847.48		$915.2930	$915.29	$915.35	$915.20