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	$72.85	12.691%	$82.0954	$82.10	$82.10	$82.10
Purchase #2	$129.77	5.278%	$136.6193	$136.62	$136.60	$136.60
Purchase #3	$100.44	4.641%	$105.1014	$105.10	$105.10	$105.10
Purchase #4	$246.91	13.723%	$280.7935	$280.79	$280.80	$280.80
Purchase #5	$124.72	13.684%	$141.7867	$141.79	$141.80	$141.80
Purchase #6	$156.92	12.724%	$176.8865	$176.89	$176.90	$176.90
Purchase #7	$180.75	3.139%	$186.4237	$186.42	$186.40	$186.40
7 purchase totals =	$1,012.36		$1,109.7065	$1,109.71	$1,109.70	$1,109.70