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	$17.60	12.597%	$19.8171	$19.82	$19.80	$19.80
Purchase #2	$233.31	12.748%	$263.0524	$263.05	$263.05	$263.10
Purchase #3	$234.31	10.789%	$259.5897	$259.59	$259.60	$259.60
Purchase #4	$219.81	5.310%	$231.4819	$231.48	$231.50	$231.50
Purchase #5	$104.51	9.461%	$114.3977	$114.40	$114.40	$114.40
Purchase #6	$66.63	6.387%	$70.8857	$70.89	$70.90	$70.90
Purchase #7	$92.84	8.299%	$100.5448	$100.54	$100.55	$100.50
7 purchase totals =	$969.01		$1,059.7693	$1,059.77	$1,059.80	$1,059.80