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	$111.77	6.788%	$119.3569	$119.36	$119.35	$119.40
Purchase #2	$123.27	7.748%	$132.821	$132.82	$132.80	$132.80
Purchase #3	$156.42	5.384%	$164.8417	$164.84	$164.85	$164.80
Purchase #4	$239.87	6.680%	$255.8933	$255.89	$255.90	$255.90
Purchase #5	$5.57	5.745%	$5.89	$5.89	$5.90	$5.90
Purchase #6	$162.28	5.712%	$171.5494	$171.55	$171.55	$171.50
Purchase #7	$169.84	13.146%	$192.1672	$192.17	$192.15	$192.20
7 purchase totals =	$969.02		$1,042.5195	$1,042.52	$1,042.50	$1,042.50