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	$132.60	5.179%	$139.4674	$139.47	$139.45	$139.50
Purchase #2	$59.44	8.482%	$64.4817	$64.48	$64.50	$64.50
Purchase #3	$99.67	5.395%	$105.0472	$105.05	$105.05	$105.00
Purchase #4	$38.28	12.467%	$43.0524	$43.05	$43.05	$43.10
Purchase #5	$32.43	3.331%	$33.5102	$33.51	$33.50	$33.50
Purchase #6	$168.67	10.577%	$186.5102	$186.51	$186.50	$186.50
Purchase #7	$241.44	8.121%	$261.0473	$261.05	$261.05	$261.00
7 purchase totals =	$772.53		$833.1164	$833.12	$833.10	$833.10