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	$89.66	13.825%	$102.0555	$102.06	$102.05	$102.10
Purchase #2	$114.82	3.798%	$119.1809	$119.18	$119.20	$119.20
Purchase #3	$245.37	11.741%	$274.1789	$274.18	$274.20	$274.20
Purchase #4	$140.30	11.619%	$156.6015	$156.60	$156.60	$156.60
Purchase #5	$160.54	9.802%	$176.2761	$176.28	$176.30	$176.30
Purchase #6	$247.70	13.277%	$280.5871	$280.59	$280.60	$280.60
Purchase #7	$19.73	13.784%	$22.4496	$22.45	$22.45	$22.40
7 purchase totals =	$1,018.12		$1,131.3296	$1,131.34	$1,131.40	$1,131.40