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	$247.45	13.162%	$280.0194	$280.02	$280.00	$280.00
Purchase #2	$137.66	11.616%	$153.6506	$153.65	$153.65	$153.70
Purchase #3	$12.89	6.458%	$13.7224	$13.72	$13.70	$13.70
Purchase #4	$178.27	6.839%	$190.4619	$190.46	$190.45	$190.50
Purchase #5	$104.59	7.807%	$112.7553	$112.76	$112.75	$112.80
Purchase #6	$184.85	11.646%	$206.3776	$206.38	$206.40	$206.40
Purchase #7	$141.69	7.644%	$152.5208	$152.52	$152.50	$152.50
7 purchase totals =	$1,007.40		$1,109.5080	$1,109.51	$1,109.45	$1,109.60