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	$52.35	3.668%	$54.2702	$54.27	$54.25	$54.30
Purchase #2	$199.39	10.376%	$220.0787	$220.08	$220.10	$220.10
Purchase #3	$214.97	5.680%	$227.1803	$227.18	$227.20	$227.20
Purchase #4	$232.82	10.630%	$257.5688	$257.57	$257.55	$257.60
Purchase #5	$74.83	13.366%	$84.8318	$84.83	$84.85	$84.80
Purchase #6	$52.69	12.844%	$59.4575	$59.46	$59.45	$59.50
Purchase #7	$73.52	12.801%	$82.9313	$82.93	$82.95	$82.90
7 purchase totals =	$900.57		$986.3186	$986.32	$986.35	$986.40