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	$127.65	9.558%	$139.8508	$139.85	$139.85	$139.90
Purchase #2	$77.90	5.157%	$81.9173	$81.92	$81.90	$81.90
Purchase #3	$138.74	9.418%	$151.8065	$151.81	$151.80	$151.80
Purchase #4	$227.49	4.643%	$238.0524	$238.05	$238.05	$238.10
Purchase #5	$35.55	5.150%	$37.3808	$37.38	$37.40	$37.40
Purchase #6	$37.55	12.564%	$42.2678	$42.27	$42.25	$42.30
Purchase #7	$165.37	12.260%	$185.6444	$185.64	$185.65	$185.60
7 purchase totals =	$810.25		$876.9200	$876.92	$876.90	$877.00