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	$242.59	10.708%	$268.5665	$268.57	$268.55	$268.60
Purchase #2	$89.59	12.760%	$101.0217	$101.02	$101.00	$101.00
Purchase #3	$173.80	13.291%	$196.8998	$196.90	$196.90	$196.90
Purchase #4	$35.43	9.688%	$38.8625	$38.86	$38.85	$38.90
Purchase #5	$33.67	5.860%	$35.6431	$35.64	$35.65	$35.60
Purchase #6	$231.97	11.372%	$258.3496	$258.35	$258.35	$258.30
Purchase #7	$192.40	3.735%	$199.5861	$199.59	$199.60	$199.60
7 purchase totals =	$999.45		$1,098.9293	$1,098.93	$1,098.90	$1,098.90