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	$42.28	12.324%	$47.4906	$47.49	$47.50	$47.50
Purchase #2	$231.93	10.292%	$255.8002	$255.80	$255.80	$255.80
Purchase #3	$98.26	10.397%	$108.4761	$108.48	$108.50	$108.50
Purchase #4	$102.27	11.774%	$114.3113	$114.31	$114.30	$114.30
Purchase #5	$149.32	6.127%	$158.4688	$158.47	$158.45	$158.50
Purchase #6	$37.90	7.641%	$40.7959	$40.80	$40.80	$40.80
Purchase #7	$34.61	4.843%	$36.2862	$36.29	$36.30	$36.30
7 purchase totals =	$696.57		$761.6291	$761.64	$761.65	$761.70