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	$49.83	10.815%	$55.2191	$55.22	$55.20	$55.20
Purchase #2	$143.51	8.774%	$156.1016	$156.10	$156.10	$156.10
Purchase #3	$221.70	4.566%	$231.8228	$231.82	$231.80	$231.80
Purchase #4	$76.31	5.627%	$80.604	$80.60	$80.60	$80.60
Purchase #5	$24.76	10.406%	$27.3365	$27.34	$27.35	$27.30
Purchase #6	$163.82	11.539%	$182.7232	$182.72	$182.70	$182.70
Purchase #7	$35.38	9.184%	$38.6293	$38.63	$38.65	$38.60
7 purchase totals =	$715.31		$772.4365	$772.43	$772.40	$772.30