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	$142.37	9.795%	$156.3151	$156.32	$156.30	$156.30
Purchase #2	$126.74	12.575%	$142.6776	$142.68	$142.70	$142.70
Purchase #3	$163.88	13.841%	$186.5626	$186.56	$186.55	$186.60
Purchase #4	$226.59	13.714%	$257.6646	$257.66	$257.65	$257.70
Purchase #5	$236.57	7.421%	$254.1259	$254.13	$254.15	$254.10
Purchase #6	$34.55	7.276%	$37.0639	$37.06	$37.05	$37.10
Purchase #7	$248.31	7.273%	$266.3696	$266.37	$266.35	$266.40
7 purchase totals =	$1,179.01		$1,300.7793	$1,300.78	$1,300.75	$1,300.90