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	$123.55	10.469%	$136.4844	$136.48	$136.50	$136.50
Purchase #2	$29.76	11.465%	$33.172	$33.17	$33.15	$33.20
Purchase #3	$139.32	3.644%	$144.3968	$144.40	$144.40	$144.40
Purchase #4	$201.68	6.366%	$214.5189	$214.52	$214.50	$214.50
Purchase #5	$54.51	4.606%	$57.0207	$57.02	$57.00	$57.00
Purchase #6	$148.71	5.242%	$156.5054	$156.51	$156.50	$156.50
Purchase #7	$34.40	5.524%	$36.3003	$36.30	$36.30	$36.30
7 purchase totals =	$731.93		$778.3985	$778.40	$778.35	$778.40