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	$138.84	9.358%	$151.8326	$151.83	$151.85	$151.80
Purchase #2	$98.63	6.577%	$105.1169	$105.12	$105.10	$105.10
Purchase #3	$103.32	12.617%	$116.3559	$116.36	$116.35	$116.40
Purchase #4	$106.42	4.620%	$111.3366	$111.34	$111.35	$111.30
Purchase #5	$45.77	4.582%	$47.8672	$47.87	$47.85	$47.90
Purchase #6	$227.72	8.399%	$246.8462	$246.85	$246.85	$246.80
Purchase #7	$117.69	5.137%	$123.7357	$123.74	$123.75	$123.70
7 purchase totals =	$838.39		$903.0911	$903.11	$903.10	$903.00