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	$245.78	6.555%	$261.8909	$261.89	$261.90	$261.90
Purchase #2	$52.91	4.305%	$55.1878	$55.19	$55.20	$55.20
Purchase #3	$224.71	6.125%	$238.4735	$238.47	$238.45	$238.50
Purchase #4	$112.46	3.203%	$116.0621	$116.06	$116.05	$116.10
Purchase #5	$35.74	7.804%	$38.5291	$38.53	$38.55	$38.50
Purchase #6	$62.45	10.287%	$68.8742	$68.87	$68.85	$68.90
Purchase #7	$81.81	10.643%	$90.517	$90.52	$90.50	$90.50
7 purchase totals =	$815.86		$869.5346	$869.53	$869.50	$869.60