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	$49.32	12.387%	$55.4293	$55.43	$55.45	$55.40
Purchase #2	$232.86	11.419%	$259.4503	$259.45	$259.45	$259.50
Purchase #3	$95.61	7.298%	$102.5876	$102.59	$102.60	$102.60
Purchase #4	$149.49	4.853%	$156.7447	$156.74	$156.75	$156.70
Purchase #5	$98.65	7.176%	$105.7291	$105.73	$105.75	$105.70
Purchase #6	$132.90	5.121%	$139.7058	$139.71	$139.70	$139.70
Purchase #7	$71.49	13.176%	$80.9095	$80.91	$80.90	$80.90
7 purchase totals =	$830.32		$900.5563	$900.56	$900.60	$900.50