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	$85.46	4.779%	$89.5441	$89.54	$89.55	$89.50
Purchase #2	$59.58	8.649%	$64.7331	$64.73	$64.75	$64.70
Purchase #3	$221.45	10.419%	$244.5229	$244.52	$244.50	$244.50
Purchase #4	$10.46	6.373%	$11.1266	$11.13	$11.15	$11.10
Purchase #5	$127.67	11.472%	$142.3163	$142.32	$142.30	$142.30
Purchase #6	$108.27	5.785%	$114.5334	$114.53	$114.55	$114.50
Purchase #7	$132.60	6.198%	$140.8185	$140.82	$140.80	$140.80
7 purchase totals =	$745.49		$807.5949	$807.59	$807.60	$807.40