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	$107.92	7.383%	$115.8877	$115.89	$115.90	$115.90
Purchase #2	$243.48	4.727%	$254.9893	$254.99	$255.00	$255.00
Purchase #3	$73.89	6.330%	$78.5672	$78.57	$78.55	$78.60
Purchase #4	$105.57	5.789%	$111.6814	$111.68	$111.70	$111.70
Purchase #5	$175.47	6.298%	$186.5211	$186.52	$186.50	$186.50
Purchase #6	$140.63	11.772%	$157.185	$157.19	$157.20	$157.20
Purchase #7	$12.36	10.153%	$13.6149	$13.61	$13.60	$13.60
7 purchase totals =	$859.32		$918.4466	$918.45	$918.45	$918.50