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	$25.36	9.810%	$27.8478	$27.85	$27.85	$27.80
Purchase #2	$5.58	9.220%	$6.0945	$6.09	$6.10	$6.10
Purchase #3	$162.72	11.624%	$181.6346	$181.63	$181.65	$181.60
Purchase #4	$25.80	4.678%	$27.0069	$27.01	$27.00	$27.00
Purchase #5	$235.95	12.678%	$265.8637	$265.86	$265.85	$265.90
Purchase #6	$117.77	5.138%	$123.821	$123.82	$123.80	$123.80
Purchase #7	$33.57	5.694%	$35.4815	$35.48	$35.50	$35.50
7 purchase totals =	$606.75		$667.7500	$667.74	$667.75	$667.70