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	$137.56	9.304%	$150.3586	$150.36	$150.35	$150.40
Purchase #2	$103.43	8.858%	$112.5918	$112.59	$112.60	$112.60
Purchase #3	$208.67	7.768%	$224.8795	$224.88	$224.90	$224.90
Purchase #4	$115.75	13.594%	$131.4851	$131.49	$131.50	$131.50
Purchase #5	$80.74	3.330%	$83.4286	$83.43	$83.45	$83.40
Purchase #6	$198.92	7.315%	$213.471	$213.47	$213.45	$213.50
Purchase #7	$66.43	9.136%	$72.499	$72.50	$72.50	$72.50
7 purchase totals =	$911.50		$988.7136	$988.72	$988.75	$988.80