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	$190.83	12.685%	$215.0368	$215.04	$215.05	$215.00
Purchase #2	$228.32	10.318%	$251.8781	$251.88	$251.90	$251.90
Purchase #3	$241.73	3.390%	$249.9246	$249.92	$249.90	$249.90
Purchase #4	$54.89	13.635%	$62.3743	$62.37	$62.35	$62.40
Purchase #5	$51.45	5.577%	$54.3194	$54.32	$54.30	$54.30
Purchase #6	$123.53	4.727%	$129.3693	$129.37	$129.35	$129.40
Purchase #7	$39.43	12.800%	$44.477	$44.48	$44.50	$44.50
7 purchase totals =	$930.18		$1,007.3795	$1,007.38	$1,007.35	$1,007.40