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	$82.53	9.820%	$90.6344	$90.63	$90.65	$90.60
Purchase #2	$237.92	7.557%	$255.8996	$255.90	$255.90	$255.90
Purchase #3	$155.86	4.297%	$162.5573	$162.56	$162.55	$162.60
Purchase #4	$168.82	10.382%	$186.3469	$186.35	$186.35	$186.30
Purchase #5	$127.85	13.760%	$145.4422	$145.44	$145.45	$145.40
Purchase #6	$246.27	9.262%	$269.0795	$269.08	$269.10	$269.10
Purchase #7	$175.45	7.265%	$188.1964	$188.20	$188.20	$188.20
7 purchase totals =	$1,194.70		$1,298.1563	$1,298.16	$1,298.20	$1,298.10