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	$19.93	9.726%	$21.8684	$21.87	$21.85	$21.90
Purchase #2	$207.76	10.410%	$229.3878	$229.39	$229.40	$229.40
Purchase #3	$159.27	13.367%	$180.5596	$180.56	$180.55	$180.60
Purchase #4	$59.95	6.646%	$63.9343	$63.93	$63.95	$63.90
Purchase #5	$35.37	6.286%	$37.5934	$37.59	$37.60	$37.60
Purchase #6	$96.69	3.699%	$100.2666	$100.27	$100.25	$100.30
Purchase #7	$153.43	10.442%	$169.4512	$169.45	$169.45	$169.50
7 purchase totals =	$732.40		$803.0613	$803.06	$803.05	$803.20