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	$38.77	4.652%	$40.5736	$40.57	$40.55	$40.60
Purchase #2	$9.99	10.412%	$11.0302	$11.03	$11.05	$11.00
Purchase #3	$227.85	5.469%	$240.3111	$240.31	$240.30	$240.30
Purchase #4	$142.92	9.720%	$156.8118	$156.81	$156.80	$156.80
Purchase #5	$28.48	13.675%	$32.3746	$32.37	$32.35	$32.40
Purchase #6	$18.36	13.690%	$20.8735	$20.87	$20.85	$20.90
Purchase #7	$93.31	10.483%	$103.0917	$103.09	$103.10	$103.10
7 purchase totals =	$559.68		$605.0665	$605.05	$605.00	$605.10