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	$242.42	12.481%	$272.6764	$272.68	$272.70	$272.70
Purchase #2	$77.40	10.678%	$85.6648	$85.66	$85.65	$85.70
Purchase #3	$142.68	7.166%	$152.9044	$152.90	$152.90	$152.90
Purchase #4	$145.94	3.187%	$150.5911	$150.59	$150.60	$150.60
Purchase #5	$29.98	10.407%	$33.1	$33.10	$33.10	$33.10
Purchase #6	$53.85	11.291%	$59.9302	$59.93	$59.95	$59.90
Purchase #7	$103.31	10.166%	$113.8125	$113.81	$113.80	$113.80
7 purchase totals =	$795.58		$868.6794	$868.67	$868.70	$868.70