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	$108.48	7.659%	$116.7885	$116.79	$116.80	$116.80
Purchase #2	$245.82	11.523%	$274.1458	$274.15	$274.15	$274.10
Purchase #3	$112.49	3.676%	$116.6251	$116.63	$116.65	$116.60
Purchase #4	$162.86	6.628%	$173.6544	$173.65	$173.65	$173.70
Purchase #5	$127.27	11.626%	$142.0664	$142.07	$142.05	$142.10
Purchase #6	$226.35	6.111%	$240.1822	$240.18	$240.20	$240.20
Purchase #7	$76.42	4.697%	$80.0094	$80.01	$80.00	$80.00
7 purchase totals =	$1,059.69		$1,143.4718	$1,143.48	$1,143.50	$1,143.50