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	$58.58	13.351%	$66.401	$66.40	$66.40	$66.40
Purchase #2	$143.48	12.108%	$160.8526	$160.85	$160.85	$160.90
Purchase #3	$247.51	10.508%	$273.5184	$273.52	$273.50	$273.50
Purchase #4	$41.94	13.789%	$47.7231	$47.72	$47.70	$47.70
Purchase #5	$38.52	11.794%	$43.063	$43.06	$43.05	$43.10
Purchase #6	$37.71	10.718%	$41.7518	$41.75	$41.75	$41.80
Purchase #7	$179.41	11.608%	$200.2359	$200.24	$200.25	$200.20
7 purchase totals =	$747.15		$833.5458	$833.54	$833.50	$833.60