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	$246.60	13.566%	$280.0538	$280.05	$280.05	$280.10
Purchase #2	$12.60	3.598%	$13.0533	$13.05	$13.05	$13.10
Purchase #3	$124.57	5.119%	$130.9467	$130.95	$130.95	$130.90
Purchase #4	$52.87	3.255%	$54.5909	$54.59	$54.60	$54.60
Purchase #5	$138.80	12.630%	$156.3304	$156.33	$156.35	$156.30
Purchase #6	$59.63	8.813%	$64.8852	$64.89	$64.90	$64.90
Purchase #7	$58.87	5.367%	$62.0296	$62.03	$62.05	$62.00
7 purchase totals =	$693.94		$761.8899	$761.89	$761.95	$761.90