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	$75.66	3.622%	$78.4004	$78.40	$78.40	$78.40
Purchase #2	$53.50	3.351%	$55.2928	$55.29	$55.30	$55.30
Purchase #3	$193.81	11.315%	$215.7396	$215.74	$215.75	$215.70
Purchase #4	$250.97	11.627%	$280.1503	$280.15	$280.15	$280.20
Purchase #5	$153.81	3.129%	$158.6227	$158.62	$158.60	$158.60
Purchase #6	$217.57	10.385%	$240.1646	$240.16	$240.15	$240.20
Purchase #7	$180.90	9.685%	$198.4202	$198.42	$198.40	$198.40
7 purchase totals =	$1,126.22		$1,226.7906	$1,226.78	$1,226.75	$1,226.80