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	$238.35	10.509%	$263.3982	$263.40	$263.40	$263.40
Purchase #2	$172.77	9.584%	$189.3283	$189.33	$189.35	$189.30
Purchase #3	$80.72	10.630%	$89.3005	$89.30	$89.30	$89.30
Purchase #4	$100.68	3.792%	$104.4978	$104.50	$104.50	$104.50
Purchase #5	$178.83	5.248%	$188.215	$188.22	$188.20	$188.20
Purchase #6	$5.38	3.488%	$5.5677	$5.57	$5.55	$5.60
Purchase #7	$99.52	4.400%	$103.8989	$103.90	$103.90	$103.90
7 purchase totals =	$876.25		$944.2064	$944.22	$944.20	$944.20