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	$44.69	12.706%	$50.3683	$50.37	$50.35	$50.40
Purchase #2	$131.26	9.538%	$143.7796	$143.78	$143.80	$143.80
Purchase #3	$84.94	6.610%	$90.5545	$90.55	$90.55	$90.60
Purchase #4	$45.54	12.280%	$51.1323	$51.13	$51.15	$51.10
Purchase #5	$9.37	3.578%	$9.7053	$9.71	$9.70	$9.70
Purchase #6	$185.91	12.411%	$208.9833	$208.98	$209.00	$209.00
Purchase #7	$30.48	4.530%	$31.8607	$31.86	$31.85	$31.90
7 purchase totals =	$532.19		$586.3840	$586.38	$586.40	$586.50