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	$26.96	11.815%	$30.1453	$30.15	$30.15	$30.10
Purchase #2	$112.70	3.499%	$116.6434	$116.64	$116.65	$116.60
Purchase #3	$96.53	4.182%	$100.5669	$100.57	$100.55	$100.60
Purchase #4	$168.89	6.456%	$179.7935	$179.79	$179.80	$179.80
Purchase #5	$62.85	11.473%	$70.0608	$70.06	$70.05	$70.10
Purchase #6	$84.57	9.824%	$92.8782	$92.88	$92.90	$92.90
Purchase #7	$53.71	5.241%	$56.5249	$56.52	$56.50	$56.50
7 purchase totals =	$606.21		$646.6130	$646.61	$646.60	$646.60