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	$179.75	4.779%	$188.3403	$188.34	$188.35	$188.30
Purchase #2	$193.54	5.128%	$203.4647	$203.46	$203.45	$203.50
Purchase #3	$19.61	10.220%	$21.6141	$21.61	$21.60	$21.60
Purchase #4	$35.33	13.694%	$40.1681	$40.17	$40.15	$40.20
Purchase #5	$7.83	12.262%	$8.7901	$8.79	$8.80	$8.80
Purchase #6	$240.68	10.218%	$265.2727	$265.27	$265.25	$265.30
Purchase #7	$54.81	8.724%	$59.5916	$59.59	$59.60	$59.60
7 purchase totals =	$731.55		$787.2416	$787.23	$787.20	$787.30