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	$247.41	10.540%	$273.487	$273.49	$273.50	$273.50
Purchase #2	$108.41	9.253%	$118.4412	$118.44	$118.45	$118.40
Purchase #3	$226.91	7.509%	$243.9487	$243.95	$243.95	$243.90
Purchase #4	$236.55	8.744%	$257.2339	$257.23	$257.25	$257.20
Purchase #5	$28.98	12.460%	$32.5909	$32.59	$32.60	$32.60
Purchase #6	$87.83	13.208%	$99.4306	$99.43	$99.45	$99.40
Purchase #7	$73.39	12.434%	$82.5153	$82.52	$82.50	$82.50
7 purchase totals =	$1,009.48		$1,107.6476	$1,107.65	$1,107.70	$1,107.50