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	$43.39	3.736%	$45.0111	$45.01	$45.00	$45.00
Purchase #2	$29.27	8.387%	$31.7249	$31.72	$31.70	$31.70
Purchase #3	$45.28	12.592%	$50.9817	$50.98	$51.00	$51.00
Purchase #4	$132.81	3.829%	$137.8953	$137.90	$137.90	$137.90
Purchase #5	$50.63	7.663%	$54.5098	$54.51	$54.50	$54.50
Purchase #6	$176.94	7.201%	$189.6814	$189.68	$189.70	$189.70
Purchase #7	$130.59	3.249%	$134.8329	$134.83	$134.85	$134.80
7 purchase totals =	$608.91		$644.6371	$644.63	$644.65	$644.60