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	$209.87	6.328%	$223.1506	$223.15	$223.15	$223.20
Purchase #2	$105.78	8.339%	$114.601	$114.60	$114.60	$114.60
Purchase #3	$226.59	5.210%	$238.3953	$238.40	$238.40	$238.40
Purchase #4	$12.49	9.698%	$13.7013	$13.70	$13.70	$13.70
Purchase #5	$143.27	6.328%	$152.3361	$152.34	$152.35	$152.30
Purchase #6	$223.45	7.651%	$240.5462	$240.55	$240.55	$240.50
Purchase #7	$130.34	12.568%	$146.7211	$146.72	$146.70	$146.70
7 purchase totals =	$1,051.79		$1,129.4516	$1,129.46	$1,129.45	$1,129.40