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	$204.76	10.622%	$226.5096	$226.51	$226.50	$226.50
Purchase #2	$139.83	11.862%	$156.4166	$156.42	$156.40	$156.40
Purchase #3	$154.45	10.444%	$170.5808	$170.58	$170.60	$170.60
Purchase #4	$135.87	4.825%	$142.4257	$142.43	$142.45	$142.40
Purchase #5	$109.33	4.121%	$113.8355	$113.84	$113.85	$113.80
Purchase #6	$206.88	12.858%	$233.4806	$233.48	$233.50	$233.50
Purchase #7	$208.89	13.624%	$237.3492	$237.35	$237.35	$237.30
7 purchase totals =	$1,160.01		$1,280.5980	$1,280.61	$1,280.65	$1,280.50