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	$11.79	6.452%	$12.5507	$12.55	$12.55	$12.60
Purchase #2	$206.56	10.277%	$227.7882	$227.79	$227.80	$227.80
Purchase #3	$77.84	9.846%	$85.5041	$85.50	$85.50	$85.50
Purchase #4	$30.56	10.111%	$33.6499	$33.65	$33.65	$33.60
Purchase #5	$65.83	10.184%	$72.5341	$72.53	$72.55	$72.50
Purchase #6	$33.94	7.453%	$36.4695	$36.47	$36.45	$36.50
Purchase #7	$164.63	5.457%	$173.6139	$173.61	$173.60	$173.60
7 purchase totals =	$591.15		$642.1104	$642.10	$642.10	$642.10