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	4.327%	$51.4541	$51.45	$51.45	$51.50
Purchase #2	$92.91	13.510%	$105.4621	$105.46	$105.45	$105.50
Purchase #3	$98.68	7.193%	$105.7781	$105.78	$105.80	$105.80
Purchase #4	$5.79	4.756%	$6.0654	$6.07	$6.05	$6.10
Purchase #5	$47.39	3.613%	$49.1022	$49.10	$49.10	$49.10
Purchase #6	$95.81	4.731%	$100.3428	$100.34	$100.35	$100.30
Purchase #7	$149.38	12.511%	$168.0689	$168.07	$168.05	$168.10
7 purchase totals =	$539.28		$586.2736	$586.27	$586.25	$586.40