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	$49.72	10.408%	$54.8949	$54.89	$54.90	$54.90
Purchase #2	$234.43	5.256%	$246.7516	$246.75	$246.75	$246.80
Purchase #3	$198.28	4.760%	$207.7181	$207.72	$207.70	$207.70
Purchase #4	$78.70	13.676%	$89.463	$89.46	$89.45	$89.50
Purchase #5	$98.78	10.219%	$108.8743	$108.87	$108.85	$108.90
Purchase #6	$126.83	5.431%	$133.7181	$133.72	$133.70	$133.70
Purchase #7	$47.61	4.718%	$49.8562	$49.86	$49.85	$49.90
7 purchase totals =	$834.35		$891.2762	$891.27	$891.20	$891.40