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	$150.79	6.677%	$160.8582	$160.86	$160.85	$160.90
Purchase #2	$156.95	12.722%	$176.9172	$176.92	$176.90	$176.90
Purchase #3	$122.68	10.865%	$136.0092	$136.01	$136.00	$136.00
Purchase #4	$167.56	13.415%	$190.0382	$190.04	$190.05	$190.00
Purchase #5	$134.95	8.771%	$146.7865	$146.79	$146.80	$146.80
Purchase #6	$88.85	13.645%	$100.9736	$100.97	$100.95	$101.00
Purchase #7	$156.52	5.367%	$164.9204	$164.92	$164.90	$164.90
7 purchase totals =	$978.30		$1,076.5033	$1,076.51	$1,076.45	$1,076.50