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	$164.67	11.682%	$183.9067	$183.91	$183.90	$183.90
Purchase #2	$43.54	3.433%	$45.0347	$45.03	$45.05	$45.00
Purchase #3	$250.72	11.767%	$280.2222	$280.22	$280.20	$280.20
Purchase #4	$48.79	3.396%	$50.4469	$50.45	$50.45	$50.40
Purchase #5	$229.57	11.158%	$255.1854	$255.19	$255.20	$255.20
Purchase #6	$157.28	6.584%	$167.6353	$167.64	$167.65	$167.60
Purchase #7	$14.47	3.412%	$14.9637	$14.96	$14.95	$15.00
7 purchase totals =	$909.04		$997.3949	$997.40	$997.40	$997.30